The iTune Remote App has stopped finding my iTunes library when connected to wifi from my main router, but works fine when connected via second wifi router on the same network (different SSID)

I'm running iTunes Remote App from a couple of iPhone 5's and a first generation iPod Touch. iTunes is running on a PC - Windows 7. My home network runs two Wifi Routers, each with a different SSID. I've had no problems with the Remote app running this set up for the last 8 months but recently the App can only find my iTunes library when the iPhone/iPod is connected via one specific router, when connected to the network via the other router, no iTunes library is found. I'm also running an Apple TV and it's the same as the iTunes Library, only visible via the one SSID.

Everything else seems to work fine when connected via either router, eg Internet on the iPhones (definitely via wifi)

I've tried renewing the lease on the iPhone wifi connection, restarting everything.....several times.....

It used to work fine, this only seems to have been a problem in recent weeks

Any help or advice would be much appreciated

Thanks

Ian