sql2005 database restore from another sql2005 backup file error.

hi

i try to restore a bak file from another sql2005 server to my sql2005 server, but it show the error message as below :

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

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ADDITIONAL INFORMATION:

Cannot open backup device 'C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Backup\backup.bak'. Operating system error 5(error not found).
RESTORE HEADERONLY is terminating abnormally. (Microsoft SQL Server, Error: 3201)

For help, click:http://go.microsoft.com/fwlink?ProdName=Microsoft+SQL+Server&ProdVer=09.00.1399&EvtSrc=MSSQLServer&EvtID=3201&LinkId=20476

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BUTTONS:

OK
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pls some one can help me ???

thanks

chaus