DB Maint Plan - Cleanup old DB Backup files not working

I created a DB Maint plan with just a 'Maintenance Cleanup Task'; the job executes fine, but does not remove files.  The sql it says it's running is: EXECUTE master.dbo.xp_delete_file 0,N'C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Backup',N'.bak',N'9/11/2005 11:12:31 AM', any ideas?  The logfile says it worked.  June CTP.