Windows Plesk 8.1 migration

I want transfer my 30+ domains from a Windows Plesk 8.1 control panel. I have tried to restore backup file I got from my old server, but it failed with a "Failed to migrate virtual server : Not a Plesk 8 backup file : Unknown compression format". I asure you that this was a plesk backup file. I may even upload it someplace you indicate.
Since Plesk 8.1 is supported as a migration format, what can I do to overcome this situation.

Closed (fixed)