Have you reviewed checklist provided in 'An SSIS package does not run when you call the SSIS package from a SQL Server Agent job step' article (http://support.microsoft.com/kb/918760)?
There is quite a few possible scenarios, where you can get 'Executed as user: DOMAIN\USERNAME. The package execution failed. The step failed.'
What is the ProtectionLevel for your package?
Have you tried scheduling really basic SSIS ?