Have you done any recent updates? Also, what OS and version of Pro Tools are you running? I've encountered this problem in a variety of ways. Sometimes I've even gotten this error after a flash drive pulled out without ejecting. When this happens in OSX 10.6.x, it causes permissions errors that severely affect Pro Tools 8. Disk Repair usually will do the trick for that. Also, the MBox2's require newer drivers, so if you haven't updated the drivers, you might also try that. The first thing I usually will try is a computer restart. I'm assuming you probably tried that (and probably some other stuff as well). Also, if you get totally stuck go to the DUC (avid.duc.com). Search your error and chances are, you'll find an answer--most likely from Avid.
Hope that helps a little.