(In case anyone else needs to fix this some day.)

It's been ages since I had to deal with "normal" remote X11 logins (ssh -X or -Y handles most of my occasional needs), but I came across an issue with XDMCP sessions hanging when talking to a roomful of newly-locked-down Solaris boxes and found this 5-year-old thread only to find that it didn't actually tell you how to fix it at the end.

Problem:

Somebody's running Cygwin's X server (XWin, not to be confused with a similar commercial product of the same name) on Windows XP, and they're using X -query (some server) to run a full "login" session off a Solaris host that's been "locked down". Fine. But when they run it, they get a black screen with an hourglass cursor and before too long, Windows tells you that Cygwin's X server is Not Responding.

Solution:

Make sure you've enabled the font server on the same host you're trying to login to (ie. the one that you have in the X -query command-line on the Windows box). The FAQ's correct in that it's a font issue, but adding -fp and pointing to another host (eg. if you just wanted to use a central box as a font server, rather than all of them) doesn't work. The hang occurs when a script that gets run at login-time on the Solaris box tries to add itself as a font server. And since the font server's not running, your X session hangs. Just make sure you restrict access to the font server port, of course!