exporting messages from windows mail

I was exporting messages from my vista laptop in preparation for the upgrade to windows 7. However when I go through the process( choosing windows mail rather than microsoft exchange), I get an error message( not enough space or corrupt file). Any ideas on what to do ?

copy the Windows Mail message folders to an external device and then move them back onto your new installation.

Alternatively pull them all into Thunderbird and use that henceforth.

Or use this method :-

"Creat a new folder on your drive named mail or such. Go to the advanced options in your mail and select to move the mail folder location.

Once the mail folder is selected allow the system to move all mail. Copy the folder to a flash drive. Go to the other Win install and copy the saved folder. Copy the mail store folder to the hard drive for the other OS. Again, go to the advanced features of mail and point the store folder to the folder you just coppied. When asked if you want to copy existing emails say yes or no depending if there may be new mails involved. Not really sure yet as to if allowing the copy of emails will or will not kill existing emails and folders. "