xdmcp broken

[Jim]

A few days ago I installed kde4 on my Kubuntu box.  Before the
installation I had xdmcp working so I could log into my kubuntu box
without having to go into the other room.  I would log in using Xming on
my windows xp box.  This worked fine.

After installing kde4 nothing happens when I try to use Xming to log in.
  Xming opens with the grey screen and the black x.  I didn't change any
firewall settings on either box.

Any ideas?

Thanks

Jim