SQL Scheduler Backup Error

Hi all,

I am using SQL Server 2005 Express version on Windows Server 2003 Small Business for my databases.  After a great deal of research on here and other website i have decided to use SQL Scheduler to manage my backups.  I have complete the setup of SQL Scheduler and i am getting an error when executing.

The script to run the back is as follows:
DECLARE @BackupName VARCHAR(255)
DECLARE @BackupFileName VARCHAR(255)

SET @BackupName = 'dbw_bentjobs_' + convert(nvarchar(20), getdate(), 112) + N'.bak'
SET @BackupFileName = 'S:\Databuild\backup\' + @BackupName

BACKUP DATABASE dbw_bentjobs TO  
DISK = @BackupFileName WITH NOFORMAT, NOINIT,  
NAME = @BackupName, SKIP, REWIND, NOUNLOAD,  STATS = 10

The error i am getting is;
The .Net SqlClient Data Provider has received a severity 16, state 1 error number 3201
on line 7 of procedure on server BHS1\SQLEXPRESS:
Cannot open backup device 'S:\Databuild\backup\dbw_bentjobs_20090428.bak'. Operating system error 3(The system cannot find the path specified.).
The .Net SqlClient Data Provider has received a severity 16, state 1 error number 3013

What could the cause of this error?