If the "remote compass not detected" message flashes to an actual heading tape every few seconds, updating your firmware with the remote compass connected will cure the problem.
If the "remote compass not detected" message is continuously on the screen, the next thing to check is the pinout between the remote compass and the EFIS using a multimeter. Since these wires are dropped into the 9 pin connector in the airplane, it's not too uncommon for one or more of them to be in the wrong spot. The correct pinout can be foundin in our installation manual.
After that, you might be looking at a hardware failure in either the EFIS or EDC. This is less likely to be the case than one of the above though.