Fredo,
I stand corrected renaming the 000_AdditionalPluginsFolder.rb did not resolve the problem, but it did expose a different/extended message:
Error Loading File C:/Program Files/SketchUp/SketchUp 2013/Plugins/FREDOTOOLS_Dir_12/__loader.rb
can't convert nil into String
Error Loading File ZLoader__GhostComp.rb
can't convert nil into String