I have checked about two dozen postings already regarding a similar problem. I used the FreePBX backup/Restore tool, the restore completed and everything seems to work other than music on hold.
I checked the conf files and they are pointing to the right path from what i see
now aside from that i actually looked at the folder itself and its owned by Asterisk and its mohmp3
I have read in some places to change to moh, and even when i changed the Conf file as well it gave me errors on the Music On Hold page so i put it back to mohmp3
I had a similar issue on another server and also the same problem, but what i did instead was convert the wav files to 8000hz PCM and then it worked, annoying to do for each file since the upload solution doesnt work, but that did the trick.
Problem is that on this other server, even this doesnt work.
Any ideas what this could be?