If anybody else had the same problem I have discovered the cause (for me) and a fix.
Cause
My Virgin Media Superhub router, without any changes by me (completely out of the box), had allowed one of the PCs on my network to configure port forwarding via uPnP for a Windows Media Player device (the PC is running Windows 7 and again, I had made no config changes to allow this to happen).
* uPnP was switched on in my router (Universal Plug & Play)
* A Windows 7 PC on the network auto configured the portmap for Windows Media Player in my router
My fix
I turned off uPnP in my router.
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I never configured anything special on my network that would cause this error - everything was due to my router and PC auto-configuring portmaps.
if you experience the same error as me, check your router.
Message was edited by: mike_edinburgh
Message was edited by: mike_edinburgh
It was a reboot of the router that allowed me to register, however as soon as I quit and restarted Sony Media Remote I had the same problem after it automatically deleted my registered device (Sony - please give more user control and don't force delete). Same error.
Another router reboot and go through registration did work again, however the same error occurred again after restarting Sony Media Remote.
Really confused now :/