I have cygwin, and have started the X server. But when I run ssh -X user@ubuntu machine, bitcoin-qt says it cannot connect to my X server.
Unless you have an X server running i WINDOWS, it doesn't matter how much forwarding you have.
I missed that cygwin has an X server. Sorry. I haven't looked at cygwin in a long time and at that time I
didn't see any X server.