What's probably causing it is this:
C:/Program Files/e-on software/LumenRT 4 Studio/LumenRT/Export/Skp/Ruby/extend_string
[The string might be curtailed by the error-report ? it probably ends with .rb or .rbs ??]
Which is probably failing to load in a 'require'...
Does it exist ?
Is that path in the $: ?
What plugin is trying to load it ?
Do you have a 'LumenRT' plugin/extension loading from one of your Plugins folders ? - if so try Disabling it in the SketchUcation Manager and restart SketchUp...
The Extensions Manager has a combined list of all Extensions, irrespective of their loading RB's location.
If you have multiple Plugins folders setup remember to use the dropdown list in the Plugins Manager, as these are listed separately 'by-folder'...
Can you type $: in the Ruby Console to see the array of available folders, from which other Ruby's can 'required'...
If the C:/Program Files/e-on software/LumenRT 4 Studio/LumenRT/Export/Skp/Ruby folder is NOT there it cannot require/load a file like ' extend_string.rb'
Have you recently messed about with the LumenRT installation ?