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.
I've also tried with Xming.
Perhaps I'm not setting DISPLAY properly before running bitcoin-qt? I've tried a number of things and I'm not certain which it should be....
I think ssh -X sets the DISPLAY at the host for you. When I last used cygwin (in 2007 I think) it worked like a charm to do X forwarding.
Note however that in any case you should be able to use the command-line bitcoind RPC calls. I do this from time to time (although GNU/Linux to GNU/Linux) and it works without any problems or caring about X.