Cannot restore SQL Differentials (SQL 2008)

Hi there

Someone managed to trash a bunch of database tables requiring a restore. So we restored the database without incident but when it comes to restoring the latest Differential Backup we get the following error;


"An exception occurred while executing a Transact-SQL statement or batch.
(Microsoft.SqlServer.ConnectionInfo)

Additional Information
The media family on device [file path] is incorrectly formed. SQL Server cannot process this media family.
RESTORE HEADERONLY is terminating abnormally. (Microsoft SQL Server, Error: 3241)"

This is appearing the second we select the source for the restore (from device). We are not even getting the to choose any options or anything.

Been at this for a couple of hours now and as you can imagine not much else is getting done.

Any ideas anyone?