I was checking through my windows security manager to make sure the new machine was blocking network access to pretty much everything - no anti virus on this machine. I noticed a listing in the Firewall I had not seen before called RENDER MANAGER, its an exe file in the Liquid Program Folder. It looks like Windows Security Center was blocking this application. I have removed this and will see what happens over the next few days.

I did stop and restart, and cleared old renders but the problem kept coming back - the above might be source of the problem.