Importing messages from Entourage into Mail

[antiuser]

My boss wants to switch to Mail from Entourage. I figured it'd be easy enough as Mail provides you the option to import messages from Entourage as you're setting it up. Except it doesn't work - my boss has a bunch of folders set up in his Entourage inbox, all of which are full of messages. Mail seems like it's importing them (the progress bar moves slowly and crunches away for line 45 minutes), but when it's all done, we only see the folders and no messages anywhere. As in, the folders are empty - Mail imported all the folder structure and account settings but none of the messages. What could be causing this? I tried doing it a second time and got the same result.