Comment 6 for bug 447431

$ xtrace -D:9 -d:0 -k 2>&1 | tee ~/xtrace.log &
[1] 20412
$ killall gnome-settings-daemon
$ DISPLAY=:9.0 gnome-settings-daemon
<scroll>
Fn+F7
The program 'gnome-settings-daemon' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadMatch (invalid parameter attributes)'.
  (Details: serial 3208 error_code 8 request_code 149 minor_code 7)
  (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.)
000:>:c88:Error 8=Match: major=7, minor=149, bad=268
000:>:0c89:32: Reply to RandrSetCrtcConfig: status=InvalidTime(0x02)
$ kill %1
$

Log attached.

BTW, there's no need to enable TCP connections in gdm to do this. xtrace works just fine using Unix sockets, which is what the -d :0 specifies, after all.