I upgraded to Lion for the first time today, and when I open the Mail app it says that the existing messages need to be upgraded before I can use Mail. So I click on that and it shows a progress bar, however it just hangs about 1/4th of the way through. I've done some googling and can't seem to find any info on the problem. Has anyone else experienced this? BTW, I'm using a MobileMe/iCloud address.