You've really been messing with things, eh?
That's an error I'd be proud to get! (My personal favourite was "Mystery Error" in the logs for lpr ... genius!)
Anyway ... moving on ...
Do you get the same tab-complete problems in a raw console? Ie: the bit before the GUI?
If tab complete works fine there, then it sounds like there might be a problem with the terminal emulators, or further down the tree (to affect them all). To be honest I'm not sure what you'd have to tweak to fix it, but take a look and see what sort of common dependencies they share, and that might help you locate the source of the problem.
Good luck, and, great error message!