I have tried repairing permissions, repairing the keychain, and restarting, all to no avail.
Anyway, here's the link, in case you want to follow along there, as well.
Hi Silverstring,
did you have On My Mac account?
For some reason I cannot import any info from the mailboxes directory...
I had the same problem and here is how i fixed it.
1. Quit Mail.app
2. Open terminal and run
/Developer/Tools/SetFile -a -v /Users/username/Library/
to make the Library folder visible as it is hidden as of 10.6.7
3. Go to /Users/username/Library/Mail and delete everything in V2 folder
(copy the contents so you don't loose emails)
4. System Preferences -> Internet and wireless -> Mail,Contacts & calendars (new on Lion)
5. Remove all accounts
6. Open mail. It should start normally now and will be empty
7. Add all accounts for Mail,contacts & calendars
8 Copy your emails back to their folders (Mail will replace all deleted folders as new one. You just copy the contents)
You guys are not going to BELIEVE what the solution is.
I tried it, though, and it worked for me.
https://discussions.apple.com/thread/3189729?start=15&tstart=0