-bash: ./av_scan.sh: Permission denied
root@omv:/media/data/usenet/scripts# ls -lah av_scan.sh
-rwxr-xr-x 1 root root 71 Jul 9 23:20 av_scan.sh
Fought with it for a couple of hours on and off before I realised what might be going on:
The OpenMediaVault developer made a decision that nothing on the "data" filesystem should be allowed to be executed. I understand why it might be best for it to be that way, so I relocated the scripts to a directory on another filesystem, and everything works as it should.