Joel

I am not sure if I can be of any help here. But anyway, here it comes.

- Have you looked at the Brown Out settings? Try to disable it for a while to see if that is the cause.

- another item you can miss out on is the layout of your board. May happen that the heavy current is flowing past your PIC and lifting the ground. I would expect the layout to follow this route if possible or else have a star point grounding
MCU -> ULN -> relay -> PS (ground / VCC) This keeps the heavy load near the Power Supply (PS)
In one case I had a problem where the layout was causing problems.

I dont know if you understand what I am saying. What has to happen is that the lowest ohmic path should be from PS to relay and then to the lighter loads.

Excuse me if these are lame suggestions and you have them sorted out

Jerson