Hi enzo - welcome to the forums.
Perhaps you have a mismatch in the type of radios you have got installed in the panel(s) and what the radio section defines in the aircraft.cfg file.
Make a backup of the .cfg file and open it in Notepad or similar. The radios section should look something like this:
[Radios]
// Radio Type=available, standby frequency, has glide slope
Audio.1=1
Com.1=1, 1
Com.2=1, 1
Nav.1=1, 1, 1
Nav.2=1, 1, 0
Adf.1=1
Transponder.1=1
Marker.1=1
If your panel contains radios with a switchable standby frequency (like the default Boeings) then the settings should be as above. If you don't have a standby on your radios then you will need to edit the second '1' in the Com and Nav lines to '0'.
Save, and that should do it.
