I had the same issue, with emphasis on had
After updating Metasploit, you need to run this to fix your db_driver issues:
It'll reinstall ROR with all it's dependencies, which appears to fix the problem.Code:sudo gem install rails --include-dependencies
I figured it out when I noticed that the console launched from the webgui of Metasploit seemed to load db_driver and execute db_ commands just fine, after a little bit of digging in the webgui folder I traced the issue back to ROR. Reinstalling it seems to do the job.