THANKS to all for your efforts!
Now it works!!! it's slower than before, but it runs and that's the main thing!
@Dan: Thank you, you're the best! ^^

Dan, i have to correct myself: It works, when i load the script from the Ruby Console = step forward! [Edit:] i just noticed, this is what thomthom meant. [/Edit]
But it doesn't work yet, when i want to load the script from the plugin-folder by starting SU normally and the script is located in the plugin-folder.

@Dan: Thank you. Now my code looks like:

require 'sketchup.rb'

module Chris88

  module LineA

    TIMER = nil

    def self.create_line()
      # delete lines 1-4 with loop
      #
       model = Sketchup.active_model
       entities = model.active_entities
#--------------------------------------------------------------------------
       # Add the group to the entities in the model
       group = entities.add_group
       # Get the entities within the group
       # alle Objekte die den entities2 zugeordnet werden, werden automatisch zu einer gemeinsamen Gruppe gemacht
       entities2 = group.entities
      
      begin
        model.start_operation( 'LineA' )
        
        @width_small = 55 # 55  
        @depth_small = 45 # 45  
        @height_small = 30 # 30 
        @width_big = 70 # 70 
        @depth_big = 60 # 60
        @height_big = 70 # 40
    
        @height_line = (4/3) * @height_small
        @radius = 1
        @arcradius = 3        
#--------------------------------------------------------------------------   
        @mat_linie=model.materials.add("Material_Linie")
        @mat_linie.color=Sketchup;;Color.new(124,252,0)  # => LawnGreen
#--------------------------------------------------------------------------
        @anzahl_arcs = ((@depth_small-6)/6).to_i
    
        @pts =[]
        @helpvar_depth = 3
        @helpvar_pts = 1
        @helpvar_baseline = 1
        @helpvar_basearc = 1     
#--------------------------------------------------------------------------
       1.upto(@anzahl_arcs) do |x|
        @helpvar2_pts = @helpvar_pts +1
#--------------------------------------------------------------------------
       if (x%2 > 0)
        @pts[@helpvar_pts] = [((@width_big-@width_small)/2)+5.35, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        @pts[@helpvar_pts+1] = [@width_small+((@width_big-@width_small)/2)-5.3, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        # arc_point
        @pts[@helpvar_pts+2] = [@width_small+((@width_big-@width_small)/2)-5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+3), @height_line]
          
        arc_circle_odd = entities2.add_circle @pts[@helpvar_pts+1], X_AXIS, @radius, 42 
        arc_circle_face_odd = entities2.add_face arc_circle_odd
        arc_circle_face_odd.material = @mat_linie
        arc_circle_face_odd.back_material = @mat_linie

        line_circle_odd = entities2.add_circle @pts[@helpvar_pts], X_AXIS, @radius, 42 
        line_circle_face_odd = entities2.add_face line_circle_odd
        line_circle_face_odd.material = @mat_linie
        line_circle_face_odd.back_material = @mat_linie

        @helpvar_baseline_odd = entities2.add_line @pts[@helpvar_pts], @pts[@helpvar_pts+1]

        @helpvar_basearc_odd = entities2.add_arc @pts[@helpvar_pts+2],[0,-1,0],[0,0,1],@arcradius,-5.degrees,185.degrees 
        
        arc_circle_face_odd.followme @helpvar_basearc_odd
        line_circle_face_odd.followme @helpvar_baseline_odd
        
#--------------------------------------------------------------------------
      elsif (x%2 == 0) 
        @pts[@helpvar2_pts-1] = [((@width_big-@width_small)/2)+5.3, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        @pts[@helpvar2_pts] = [@width_small+((@width_big-@width_small)/2)-5.35, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        # arc_point
        @pts[@helpvar2_pts+1] = [((@width_big-@width_small)/2)+5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+3), @height_line]
              
        arc_circle_even = entities2.add_circle @pts[@helpvar2_pts-1], X_AXIS, @radius, 42 
        arc_circle_face_even = entities2.add_face arc_circle_even
        arc_circle_face_even.material = @mat_linie
        arc_circle_face_even.back_material = @mat_linie
        
        line_circle_even = entities2.add_circle @pts[@helpvar2_pts], X_AXIS, @radius, 42 
        line_circle_face_even = entities2.add_face line_circle_even
        line_circle_face_even.material = @mat_linie
        line_circle_face_even.back_material = @mat_linie
                
        @helpvar_baseline_even = entities2.add_line @pts[@helpvar2_pts], @pts[@helpvar2_pts-1]

        @helpvar_basearc_even = entities2.add_arc @pts[@helpvar2_pts+1],[0,1,0],[0,0,1],@arcradius,-5.degrees,185.degrees
        
        arc_circle_face_even.followme @helpvar_basearc_even
        line_circle_face_even.followme @helpvar_baseline_even
        
      end # if
#--------------------------------------------------------------------------
      if (x == @anzahl_arcs)
        @pts[@helpvar_pts] = [((@width_big-@width_small)/2)+5.35, ((@depth_big-@depth_small)/2)+(@helpvar_depth+6), @height_line]
        @pts[@helpvar_pts+1] = [@width_small+((@width_big-@width_small)/2)-5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+6), @height_line]
        
        @helpvar_baseline_ende = entities2.add_line @pts[@helpvar_pts], @pts[@helpvar_pts+1]
        
        line_circle_odd = entities2.add_circle @pts[@helpvar_pts], X_AXIS, @radius, 42 
        line_circle_face_odd = entities2.add_face line_circle_odd
        line_circle_face_odd.material = @mat_linie
        line_circle_face_odd.back_material = @mat_linie

        line_circle_face_odd.followme @helpvar_baseline_ende
        
      end # if
#--------------------------------------------------------------------------
      @helpvar_depth = @helpvar_depth + 6
      @helpvar_pts = @helpvar_pts + 3
#--------------------------------------------------------------------------
    end # upto - do    
    
#--------------------------------------------------------------------------        
      rescue => e
        model.abort_operation
        puts("#{Module.nesting[0].name} Error #<#{e.class.name}; #{e.message}>")
        puts(e.backtrace)
      else
        model.commit_operation
      end
    end # def

  end # module LineA


  # run when file loads
  #
  if Sketchup.active_model &&
  Sketchup.active_model.active_entities
    LineA.create_line
  else
    LineA;;TIMER = UI.start_timer(2.0, true){
      if Sketchup.active_model &&
      Sketchup.active_model.active_entities
        UI.stop_timer(LineA;;TIMER)
        LineA.create_line
      end #if
    }
  end

end # module Chris88

Is this what do you mean?
However it doesn't solve the bug.

@thomthom: Thanks, that could help me. I know this, what you wrote in your sidenode, but it didn't work: When i draw a circle and a path, which starts at the central point of the cricle, Sketchup draw only the lines, but not the curves. This is why i decided alternatively to draw the lines and the curves seperately. Do you think the gaps could be the reason for the bug?

@thomthom: Correct. And yes, it crashes if it's located in the plugin-folder, too.
And it doesn't matter, if i load the script with the Ruby Console or if i start SU normally and the script is in the plugin-folder.

@Dan: Thanks Dan! I will test it in a few minutes...

The course of action of my program, which conduces to woodworking:
in C#:

• read technical values out of xml-files
• generate a rubyscript for every object
  (tool, wood, machining line,...) in .txt- format
• replace the wildcards (i.e: width,height,depth of a wooden box)
• put all rubyscripts together an name the file xy.rb
• start Sketchup with the file xy.rb as argument

... and my code is all but finished, when i start SU with the file xy.rb it crashes and SU reports a "bug splat"
http://images.wikia.com/sketchyphysics/images/6/63/BugSplat.png

So because i'm almost at the end of coding my program, i actually don't want to modify the rubyscript, that it loads premade components.

@thomthom: i can start successfully the script in SU per Ruby Code Editor or per Sketchup Bridge in RDE to test it. The error appears when i copy my script in the plugin-folder, load it from ruby console in SU or start SU per cmd and assign my script as parameter in the cmd.

@TIG: thanks for your corrected code and suggestion, but it doesn't solve the bug. And i don't 'understand' your first lines: "make a new template containing the desired stuff as the default" ... and it shouldn't be premade components (that's was my first attempt )

the strange loop ist an advice of TIG... http://forums.sketchucation.com/viewtopic.php?f=180&t=41767,
it makes sure that all services of SU are loaded succesfully.
it runs also without this loop.

And i have commenting out all loops and many lines, but i didn't found the failure.
It's strange that i can run the script succesfully in SU, this bug is only when loading the script out of the plugins or starting SU per cmd with the script as parameter.

(P.S. i have SU 8 free version)

Hi all,
i have this code (i know it looks confusing, because i don't know
how to program the 'followme'-function, but it's not the problem)

 module LineA
  def LineA.create_line
  unless Sketchup.active_model;
    until Sketchup.active_model.active_entities
    end
  end
  
    model = Sketchup.active_model
    entities = model.active_entities
#--------------------------------------------------------------------------
    # Add the group to the entities in the model
    group = entities.add_group

    # Get the entities within the group
    entities2 = group.entities
#--------------------------------------------------------------------------
    @width_small = 55 # 55  
    @depth_small = 45 # 45  
    @height_small = 30 # 30 
    @width_big = 70 # 70 
    @depth_big = 60 # 60
    @height_big = 70 # 40
    
    @height_line = (4/3) * @height_small
    @radius = 1
    @arcradius = 3
#--------------------------------------------------------------------------
    @mat_linie=model.materials.add("Material_Linie")
    @mat_linie.color=Sketchup;;Color.new(124,252,0)  # => LawnGreen
#--------------------------------------------------------------------------
    @anzahl_arcs = ((@depth_small-6)/6).to_i
    
    @pts =[]
    @helpvar_depth = 3
    @helpvar_pts = 1
    @helpvar_baseline = 1
    @helpvar_basearc = 1 
    
#--------------------------------------------------------------------------    
    1.upto(@anzahl_arcs) do |x|
      @helpvar2_pts = @helpvar_pts +1 
#--------------------------------------------------------------------------
      if (x%2 > 0)
        @pts[@helpvar_pts] = [((@width_big-@width_small)/2)+5.35, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        @pts[@helpvar_pts+1] = [@width_small+((@width_big-@width_small)/2)-5.3, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        # arc_point
        @pts[@helpvar_pts+2] = [@width_small+((@width_big-@width_small)/2)-5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+3), @height_line]
                
        arc_circle_odd = entities2.add_circle @pts[@helpvar_pts+1], X_AXIS, @radius, 42
        arc_circle_face_odd = entities2.add_face arc_circle_odd
        arc_circle_face_odd.material = @mat_linie
        arc_circle_face_odd.back_material = @mat_linie
                
        line_circle_odd = entities2.add_circle @pts[@helpvar_pts], X_AXIS, @radius, 42
        line_circle_face_odd = entities2.add_face line_circle_odd
        line_circle_face_odd.material = @mat_linie
        line_circle_face_odd.back_material = @mat_linie
               
        @helpvar_baseline_odd = entities2.add_line @pts[@helpvar_pts], @pts[@helpvar_pts+1]
       
        @helpvar_basearc_odd = entities2.add_arc @pts[@helpvar_pts+2],[0,-1,0],[0,0,1],@arcradius,-5.degrees,185.degrees 
        
        arc_circle_face_odd.followme @helpvar_basearc_odd
        line_circle_face_odd.followme @helpvar_baseline_odd
        
#--------------------------------------------------------------------------
      elsif (x%2 == 0) 
        @pts[@helpvar2_pts-1] = [((@width_big-@width_small)/2)+5.3, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        @pts[@helpvar2_pts] = [@width_small+((@width_big-@width_small)/2)-5.35, ((@depth_big-@depth_small)/2)+@helpvar_depth, @height_line]
        # arc_point
        @pts[@helpvar2_pts+1] = [((@width_big-@width_small)/2)+5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+3), @height_line]
                
        arc_circle_even = entities2.add_circle @pts[@helpvar2_pts-1], X_AXIS, @radius, 42
        arc_circle_face_even = entities2.add_face arc_circle_even
        arc_circle_face_even.material = @mat_linie
        arc_circle_face_even.back_material = @mat_linie
                
        line_circle_even = entities2.add_circle @pts[@helpvar2_pts], X_AXIS, @radius, 42
        line_circle_face_even = entities2.add_face line_circle_even
        line_circle_face_even.material = @mat_linie
        line_circle_face_even.back_material = @mat_linie
                       
        @helpvar_baseline_even = entities2.add_line @pts[@helpvar2_pts], @pts[@helpvar2_pts-1]
       
        @helpvar_basearc_even = entities2.add_arc @pts[@helpvar2_pts+1],[0,1,0],[0,0,1],@arcradius,-5.degrees,185.degrees
        
        arc_circle_face_even.followme @helpvar_basearc_even
        line_circle_face_even.followme @helpvar_baseline_even
        
      end # if
#--------------------------------------------------------------------------
       if (x == @anzahl_arcs)
        @pts[@helpvar_pts] = [((@width_big-@width_small)/2)+5.35, ((@depth_big-@depth_small)/2)+(@helpvar_depth+6), @height_line]
        @pts[@helpvar_pts+1] = [@width_small+((@width_big-@width_small)/2)-5, ((@depth_big-@depth_small)/2)+(@helpvar_depth+6), @height_line]
        
        @helpvar_baseline_ende = entities2.add_line @pts[@helpvar_pts], @pts[@helpvar_pts+1]
                
        line_circle_odd = entities2.add_circle @pts[@helpvar_pts], X_AXIS, @radius, 42
        line_circle_face_odd = entities2.add_face line_circle_odd
        line_circle_face_odd.material = @mat_linie
        line_circle_face_odd.back_material = @mat_linie
                
        line_circle_face_odd.followme @helpvar_baseline_ende
        
      end # if
#--------------------------------------------------------------------------
      @helpvar_depth = @helpvar_depth + 6
      @helpvar_pts = @helpvar_pts + 3
#--------------------------------------------------------------------------
    end # upto - do    
#--------------------------------------------------------------------------
  end # def
end # module

LineA.create_line

When i execute it in SU there's no error, but if i load it in the plugins of SU,
the hole SU break down and show me a 'Bug Splat', however no significant error message.
I hope you can help me.
Thanks

Thanks to all,
the problem is solved