The backup file contains unrecognized data and cannot be used

Hi all

We really have a big issue with dozens of BKF files; we cannot restore from them. We have tried from Windows 2003 where they originally have been taken, and from Windows 2008. - No luck, we get the error "The backup file contains unrecognized data and cannot be used" during the catalog process.

What option do we have?

Thanks,

Rene