Basically I'm trying to prompt you to learn how to read Ruby error and backtrace messages. “filename:lineNo: inmethod”‘ or “filename:lineNo.”` http://ruby-doc.org/core-2.2.4/doc/syntax/exceptions_rdoc.html http://ruby-doc.org/core-2.2.4/Exception.html @medeek said: Okay 95% of that just went over my head, but I'll try and decipher into terms I can understand. https://en.wikipedia.org/wiki/Data_validation An example in Ruby of testing if an object reference is pointing at an object of a certain class: if obj.is_a?(NilClass) ... or ... if obj.is_a?(Float) An example in Ruby of validating that an object reference call responds to a certain method call: if obj.respond_to?(:methname) ... and testing for the "asterisk" method specifically: if obj.respond_to?(:*) @medeek said: But why would this error only be raised for SketchUp running on MacOS and not Windows? I don't know (offhand) as I avoid Macs myself. (But OSX and MS Windows use different sets of keycodes.) Actually, looking at the backtraces (in your original error listing) the errors are kicked off by a LButtonDown keypress, but are occurring in the `` create_timber_geometry()`' method, lines 1064 and 1355.