I had this same problem. I think what the problem was is that if you had SketchUp "Basic" installed first, when you uninstall it (if you did), it leaves many of the files behind in C:\program files\google\google sketchup 6. This is the same default location for the program file for SketchUp Pro, so I would imagine when you install Pro, it sees the files already exist and skips over them, not replacing them.
I didn't look into this but I would guess that that "Basic" doesn't include the Ruby plugins functionality so some of these files reflect that lack of support.
In any case, try uninstalling ALL versions of the program you have and then also deleting the program file and all of its contents. When I did this and did a clean install on Pro it worked fine. If for some reason you want to keep "Basic" I would imagine that re-installing Pro and specifying a different program file location would also do the trick.
Hope this helps.