Hey there -
It looks like you've probably got yourself back on the high road ... The same thing happened to me with my Exchange account. It was the only account I had setup and I was using the stock Email app. The app would continue to sync and download my messages, but if I tried to open a message the app would force close on me.
I tried deleting the account and rea-adding it ... with no luck. So I hard reset my phone and had everything set back up in about 30 minutes.
The good news is ... I have reproduced the problem and I think I can tell you why it happens. I had my Droid in Airplane Mode, because I was on a flight over the holidays to go to see my family. I accidentally opened the Email app, but then closed it. Once I got to my destination and turned airplane mode off, Emails started coming in. I tried to open one and that's when the Forced Close started happening.
After I finished setting it back up I figured I would test it again to see what actually caused the problem. I turned airplane mode back on, then opened the Email app. Shut the Droid down, booted it back up, turned airplane mode off. Went to open my emails and the Forced Close started happening again.
So now, I make sure whenever I turn airplane mode on I make sure to stay as far away from the Email app as I can.