Hi Wartender,
Was it on an E-jet? It appeared once to me while on the simulator, and changing the XPDR side solved the problem.
I understand the original message is not an EICAS one, right? In this case it will not appear on the QRH, but I did not found it on the FMS guide either. In any case I will forward the doubt to my training skipper and see what comes out.
Cheers,
BF