A couple of thoughts come to mind, but since I don't know what kind of coach the generator is installed in, I'm just guessing.
First, is the generator wired to start from the chassis or house batteries? Could it be that the battery actually wired to start the generator is not actually charged?
How are you determining that the battery is charged? You can have what appears to be a correct voltage for a charged battery, but no amperage. If you are not sure, put a digital voltmeter on the battery and have someone try to start the generator while you monitor voltage. If it drops a bunch when the generator starter is activated you either have a bad battery or a charging system that is not working.
If the batteries are actually charged and good, and you hear the solenoid clicking when attempting to start the generator, I would suspect the starter motor has failed or a connecting cable/wire has failed. Look for corrosion around the battery terminals and/or loose connections.
Good luck.
TJ