Jobs failing with the error – job can not start as it is suspended

If you look in the SQL Agent error logs it should record the problem - Subsystem %s could not be loaded.

When this happens you need to run this script:

use msdb;
delete from msdb.dbo.syssubsystems;
exec msdb.dbo.sp_verify_subsystems 1;
go

Now restart the SQL Agent

Reference

http://support.microsoft.com/?kbid=914171