Can't see local DLNA server from iPad and iPhone

Hi

I have a Windows 8.1 PC running a DLNA server which services a community of devices including Win 8.1 Laptop, XBOX One and 2 x XBOX 360 Consoles, an iPad and iPhone. All has been working until recently (within last 7 days). (I cannot recall whether the current situation immediately followed ay one particular change).

Right now all devices can still use the DLNA service apart from the iPad and iPhone. I cannot connect to the service from the iPad using a DLNA renderer or even connect to the web interface via Safari. I have tried (and failed) to ping the server from my iPad (pinging from my laptop both wired and wirelessly is fine). I have turned off the Windows firewall and still have the problem. Using a subnet pinger, my iPad does find my laptop.

I am at a loss! I have tried to isolate the issue but have failed. Sounds like a server side / firewall issue (access to a port) but other systems are fine. Seems curious it is occurring on the 2 iOS devices in the household!

Can anyone suggest a course of action?

cheers

John