MAX809 driving a mosfet
The effect of a load seems like a wiring problem of some kind, but in any case this circuit will not work very well. You have the load wired on a source follower so the MOSFET will always drop Vgs at the load current, which will vary from unit-to-unit and with the load current but typically it's more than 1V at a few mA. 

If you look at your circuit you can see that the voltage that turns the N-channel MOSFET "on" (Vgs) is the Vcc (on the output of the MAX809) minus the voltage across the load. Since it takes a couple volts to turn the MOSFET fully on you can never get anywhere near the full Vcc across the load (doesn't explain the "zero" you say you are observing though). 

What you can use is a voltage detector with active HIGH push-pull output (eg. MAX810) and a P-channel logic-level MOSFET.