I got it working. I used the ruby-c-extension-example to create a visual studio 2017 project and compiled it. You can find the VS2017 project in the link and compile it or use the so in releases if you have Sketchup 2017 x64. https://drive.google.com/open?id=1Ulz8sNDuyg2dY9Yy1vIW_thEOhAtIq2L

Can't say with absolute certainty without seeing your code, but you are most likely right about the decimal point mark causing the error. Depending on your OS and its settings, the mark may or may not automatically change when you change the input language. You may have to change the locale and reboot.

Thanks that works

As I already explained... And you can see this when it's done 'manually' too... If a rectangle face is wholly within another planar face and none of its edges are shared with any other faces, then the PushPull leaves a hole where the original face was. If a rectangle face has any edges shared with other faces - as in the case you have where the face is on the corner of the form and one edge has another non-planar face - then the PushPull can leave the original face behind in the new geometry...

I've found the problem. It was in line "opening = subelement.entities.add_group" I created a group inside the group I wanted to subtract.

Assuming you have no more need of the group or its contents use: wandgroep.erase! See here: http://ruby.sketchup.com/Sketchup/Drawingelement.html#erase%21-instance_method BUT if you want to explode it and put its contents into the group's previous context, use: wandgroep.explode See here: http://ruby.sketchup.com/Sketchup/Group.html#explode-instance_method

You should have a look at the SketchUp Team's Shapes and Window Maker example extensions. They (and a few others) use a library class called Parametric that handles creating a inputbox of parameters and saves them into an attribute dictionary attached to the (group or component) object. Why reinvent the wheel?