Unsupported
Jobs may work if using one of these plugins, however, issues involving these plugins will be unsupported. Use at your own risk.
Permission*** - Permission*** is inherently flawed, breaks Bukkit. Test with another permission manager first, chances are the issue is specific to PEX.
Spout - Spout has a history of being unstable at times, and users submit bugs here instead of to them. Remove Spout first to see if your problem goes away.
Forge/ModloaderMP mods - Test against vanilla Bukkit first. If it works with Vanilla Bukkit, then the problem is somewhere else.