I've had this issue pop up on multiple occasions (I've replicated similar results on my older backup/clone OS drive as well)...
There are two issues really:
1) Can't access Samba share from Windows 7
2) Can't access OMV web interface (403 Forbidden nginx error) - this was after attempting an update from OMV's Update Manager
Details:
(1) happened when I physically moved the fully working server to another home network (I took the server to my home, planning to do backups and to replace the RAID drives). I presume it is Windows/network related since it was working in the previous network, though this perplexes me.
This was when I tried OMV's Update Manager that I ran into more problems.
(2) happened after doing a simple update on a few samba related packages (see screenshot). I've experience the same problem when attempting to update all the packages on my other cloned drive, so I'm pretty sure problems arise after updates. The list of updates is large, presumably because I avoided updating in the past for this reason. I can't avoid updates forever. Basically what happens is after pressing upgrade the screen would get stuck. Eventually after doing nothing for a long time, I would attempt to refresh browser, and then i get the nginx error.
Your help is much appreciated!! I had the bright idea of 'working' on the server before leaving the county for a few weeks....