Do you have the very latest version of LibFredo installed ?
Yes
Do you only have it loading from one Plugins folder ??
I have no additional plugin folders
Before installing the files you provided, I compared them side by side with those already installed and they appear identical to what I had already installed.
I saw nothing in LibFredo6.plugin that mentions "UTF-8 without BOM", however the Load Error message says, " invalid byte sequence in UTF-8>" which, obviously, does not add "without BOM". Significant?
Nevertheless, I put the files you provided into:
C:\Users\jamesb\AppData\Roaming\SketchUp\SketchUp 2015\SketchUp\Plugins\Fredo6_!LibFredo6
Upon startup of SU I received the same load errors as before.
Since Lib6Core does not have line numbers I could not I could not find lines identified in Load Errors.
Error Loading File Fredo6_!LibFredo6.rb
Error: #<ArgumentError: invalid byte sequence in UTF-8>
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:702:in match' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:702:in block (2 levels) in load_from_config'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:701:in each' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:701:in block in load_from_config'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:700:in foreach' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:700:in load_from_config'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:1070:in block in load_all_plugins' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:1070:in each'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:1070:in load_all_plugins' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6/Lib6Core.rb:772:in load_from_config'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6.rb:188:in startup' C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6.rb:335:in module:LibFredo6'
C:/Users/jamesb/AppData/Roaming/SketchUp/SketchUp 2015/SketchUp/Plugins/Fredo6_!LibFredo6.rb:34:in `<top (required)>'