migrating windows live mail from one computer to another

Old PC is windows 7 home premium 32-bit running windows live mail.

New laptop is windows 7 ultimate 64-bit running windows live mail.

Both are using POP3 and receive and send through att.yahoo.com.

The laptop syncs ok for the contacts from the PC.

But I'm unable to migrate the messages and folders from the PC to the laptop.

I followed the export/import procedure from:

http://windows.microsoft.com/en-us/windows-live/mail-import-backup-restore

I used a thumb drive and created a new folder and exported to that folder.

Plugged the drive in the laptop and started the import procedure.

What moved was incomplete (folders missing, no messages, etc.)

Thumb drive says the folder has only 128kb of info and it is useless.

How do I get rid of the wrong stuff from windows live mail in the laptop?

And, how do I migrate the folders and messages from the PC to the laptop?