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

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

>
>Anyone know what's wrong here?

In addition to Naomi, check if you have the same version of SQL Server with your client.
If you have a smaller version you can't restore the backup.
Even SQL Server 2008 can't restore backups made with SQL Server 2008 R2.