Dan,
If we are talking about the Advanced Alerts then you only need it running on a single system since it is Polling Engine Agnostic. Also make sure that the trigger delay has been set on the Trigger Condition screen and not eh Alert Action screen.
Cheers,
Dan
You would recommend only having one server have the alert service running? Could having more than one run be creating DB locks?
Yes, that is a possibility, however, rare.
Cheers,Dan