xhcat-gnome refuses to start with the following message:

The program 'xchat-gnome' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadImplementation (server does not implement operation)'.
  (Details: serial 989 error_code 17 request_code 145 minor_code 5)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

I believe this may have been caused after changing the background transparency.

I went into gconf-editor and changed the "Background Transparency" setting under "Main Window" from 0.5 to 0 and the program was then able to start.