Odd thing indeed...I just created a similar type of attribute and received the same error. Mine went away by deleting /var/cache. From reading in other threads it seems that this can happen. Don’t know if you have cache enabled. I didn’t and this still did the trick.
I just cleared & disabled my cache (through Admin, not by deleting directory /var/cache), logged out of my Admin (did not close my browser), and I still can not update Attributes or Polls (Polls Problem I am having)