Sometimes it happens because of the version change like store 2012 db on 2008, so how to check it?
RESTORE VERIFYONLY FROM DISK = N'd:\yourbackup.bak'
if it gives error like:
Msg 3241, Level 16, State 13, Line 2 The media family on device 'd:\alibaba.bak' is incorrectly formed. SQL Server cannot process this media family. Msg 3013, Level 16, State 1, Line 2 VERIFY DATABASE is terminating abnormally.
Check it further:
RESTORE HEADERONLY FROM DISK = N'd:\yourbackup.bak'
BackupName is "* INCOMPLETE *", Position is "1", other fields are "NULL".
Means either your backup is corrupt or taken from newer version.