I just noticed that my solution was already posted by barree in sept2011 and is a sticky in the Plan-G forum. However, it never came up in my Google-search,
Bests, Peter

I had exactly the same situation and for two days I read all possible forum posts but without success.

Today I had an idea and that worked: After renaming my existing simconnect.xml I created a new one with the Simconnect Config Tool ( download here: http://simconnectconfigtool.codeplex.com/ ).
I ticked Create custom SimConnect settings > add > port 9017 was given automatically, I just changed the address from 0.0.0.0 to 192.168.0102 (as per FSX-PC  Control Panel > Network and Internet > Network Connections > > Local Area Connection > Details ... IPv4 Address).
After copying address and port to Plan-G the connection was immediate.

Plan-G is a great tool!

Good luck
Peter