I think you have to explain how you did that in more detail, if you don't mind.
OMV is on port 81 and everything has been working fine since I installed it last august.
I don't have ipv6 enabled though either on my router or OMV server but it has been working before april. Could this have something to do with this?
*edit* port 80 is already open between the router and omv server.