Thunderbird Tips
From menu "Tools->Options->Advanced" click on [Config. Editor]
1. Create smart mailboxes-3 inside the Mail folder in your profile directory
2. Check to see that mail.server.server(something).directory-rel have this inside it. " [ProfD]Mail/smart mailboxes-3 " and nothing else.
3. Check that the path to your smart folders are correct. Should say something like " C:\Users\username\AppData\Roaming\Thunderbird\Profiles\profile.name\Mail\smart mailboxes-3 "
If you have your profile on another drive than C: you have to make sure it points to the correct disk.
The problem seems to be that Win7 x64 stores User Application Data in a different location than WinXP.
Or mozbackup it self, problem don't seem to exist if you just copy your profile from old computer to the new one.
Bug, that really don't have to be a thunderbird bug posted and resolved in bugzilla,
here!