G5 won't wake from sleep when using keyboard or mouse

I have a PowerMac G5 2.0Ghz Dual Processor system that I m using with the newer slim Apple Keyboard and Apple Optical mouse. When I try to "wake" the G5 from sleep with either the mouse or keyboard, it wakes up, and simply goes back into sleep mode, however, if I "wake" the G5 from the power button it remains awake.

Any idea what is causing this problem?

Thanks!

G5 won't wake from sleep when using keyboard or mouse

Yes, I am running 10.5 with all the updates.