Bob,

Thanks for the reply. I do have a cap across +5 and Gnd. The program is simply

High PortC.1
YR:
Low PortC.1
High PortC.2
Pause 700
Low PortC.2
Pause 700
goto YR

I do have the WDT enabled

It will generally run for about 5 minutes, but sometimes only a few cycles, and resets to High PortC.1.

I am using a 7805 regulator, well filtered.
I have been working on the theroy that the power supply is dropping out, but it always appears to be at full power.

Thanks