I've done some more testing and I can't get 3.01-14 or 3.01-18 to work on Windows 7 x64 SP1, a lot of crashes and a few started sessions but never a fully working X window. 3.01-13 works pretty much every time.
On Windows Server 2003 SP2 (32-bit), 3.01-18 works with both Xming and vcxsrv.
Seems like the transition to libssh (which I presume is version 3.01-14 and later?) is causing trouble on 64-bit Windows 7 .
Cheers, Daniel