1. Add at least over 60 pictures to the background selecter.
2. Change your background

NOTE: I noticed some sketchy behavior with these tests when Gnome tried to
tile/scale the images to your screen. If you have over 60 added, and it doesn't
crash, exit out, go back in, and try it again. Also, try different sized
pictures as well. I could not make it crash with exactly 60 pictures added, no
matter what I did. I only tested down to 59, and that didn't crash either.

The following is the error message displayed if you ran gnome-terminal from a
command shell when this bug occured:

The program 'gnome-panel' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadGC (invalid GC parameter)'.
  (Details: serial 24035 error_code 13 request_code 62 minor_code 0)
  (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.)

Also, the error dialogue: "I've detected another panel running and will now
exit" refuses to go away. If you hit OK, it comes back up.