Sounds like you've got a corrupted gem spec, probably from the gem you're working on. My guess is that it's related to an old version of RubyGems in the old version of Ruby you're using. Whatever the gem name is, you should be able to cd into your gems dir (somewhere in ~/.rvm), kill its specifications/ and cache/ folders, and start over.
The gem spec probably needs ["lib"] instead for some entry in there…you could also just jump into the specifications/ dir and manually edit it to fix it (and then rebuild your gem so this doesn't happen anymore).
Overall this is a pretty gross bug…I'd try updating RubyGems once you're done, hopefully this won't happen in later versions.