The MRGL of the GW will allocate the MOH server. From your description looks like the MOH server does not have the custom MOH audio sources uploaded to it, and thefore is giving you dead air on any audio source beside the sample.
Check what MOH server the call is connected to with show call active voice compact, and then make sure all the MOH custom files are uploaded to the server.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...