SQL Server 2008 external disc back-up

I have an external network back up disc mapped at Y:\ , when I try to create back up on disc Y:\ I have

BACKUP DATABASE [DATABASE_NAME] TO  DISK = 'Y:\backup\backup.bak' WITH NOFORMAT, INIT,  NAME = @BackupName, SKIP, NOREWIND, NOUNLOAD,  STATS = 10

when I run it following error occurs

Msg 3201, Level 16, State 1, Procedure sp_backup, Line 10 Cannot open backup device 'Y:\backup\backup.bak'. Operating syste开发者_StackOverflow中文版m error 3(Path not found.).

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Use a UNC path (e.g. \\server\share\backup\backup.bak). Whilst you may have the Y drive mapped, the user account that SQL Server is running under doesn't. And it's that "user" that is going to perform the data access.

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It is possible that there is no folder 'backup' on drive Y: Or your account haven't appropriate permissions to this folder.