A client sent me a database (.bak) file. I'm trying to restore it. I'm getting

TITLE: Microsoft SQL Server Management Studio
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An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)

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ADDITIONAL INFORMATION:

The media family on device 'C:\Program Files (x86)\Microsoft SQL Server\MSSQL.1\MSSQL\Backup\ER_VT_backup_2011_05_10_020001_3850000.bak' is incorrectly formed. SQL Server cannot process this media family.
RESTORE HEADERONLY is terminating abnormally. (Microsoft SQL Server, Error: 3241)

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=09.00.5000&EvtSrc=MSSQLServer&EvtID=3241&LinkId=20476

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BUTTONS:

OK
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Anyone know what's wrong here?