The fan sockets on the MB are clearly labeled as cpu and system. The error is complaining about the system fan. Besides I didn't have to unplug the CPU fan during the transplant. The new case fan does have 3 wires same as the old. (New Fan = CoolerMaster A12025-12CB-3BN-F1)

There must be something plugged into the system fan jack, or I get the error. For now I've transplanted the old fan.

The transplant is from a HP media center box. The MB is made by ASUS, but its bios is lame, no options for RPM check.

I don't have a graphics card that requires additional power, So I guess I'll just coil the unused lead and tuck it out of the way. Actually, I'm tempted to just chop it to 4in, and put a molex on the stub.