SQL Server: Operating System Error 5 (Access Denied)

when i tried to bakup my sqlserver database under win serv 2003 i get a strange error

Cannot open backup device 'C:\***********'. Operating system error 5(access denied). RESTORE HEADER ONLY is terminating abnormally. (Microsoft SQL Server, Error: 3201)
	Cause
The SQL Configuration Manager cannot log in due to shared permissions issue under the executed backup account.
	Resolution
Open SQL Configuration Manager Right-click on the database instance (typically SQL Server: SRVMGRENT) and select Properties from the pop-up menu. On the Log On tab, change Built-in account to Local System. Click the OK button.