Hi - interesting situation.

Can you check this thread? http://blogs.msdn.com/b/venkn/archive/2010/03/16/failing-to-restore-sql-server-database-backup-with-internal-consistency-error.aspx

It's a db that is corrupt. Did you ask your client to run dbcc checkdb and mail you the results?

You could try to restore it with the CONTINUE_AFTER_ERROR. See Books online for details.