Error Restore of Database

HI,

While restoring a database from a backup file having extension .back we are getting the following error
"back is not part of the multiple family media set backup with format can be used to form a new media set"

Please guide me how to handle this error.

Thanks,
KarthikI have got informative link...

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=915089&SiteID=1