Answer by Fatherjack

Would have suggested db size is issue if restoring onto SQL Express but you say source is also Express edn? *edit* You state the file size as well below 10GB so, in that case you must consider its a corruption of the backup file. Does the backup get created on local disk? I would check network activity at time of backup if its copied over LAN, may be a faulty copy or it might be faulty partitions on your HDD. Have you got any HDD maintenance tools or done a checkdisk recently?