Chris,
Like Pete I run all of my lights on the cheap HD timers (I have a 400W DE and a 150DE plugged into one) without any problems. The problem may be that that particular circuit in your house feeds a whole bunch of other stuff and the DE ballast just send it over board. If you can I would reccomend plugging the ballast into a seperate circuit and see if it trips the timer. Just guessing here but I bet there is just to much load on that circuit.

-Greg