This just occurred during normal use (I doubt that I would be able to reproduce it). Lisp backtrace follows: # (condition-case ... . error) # (catch top-level ...) #0 0x403a94b1 in ?? () from /lib/libc.so.6 #1 0xbfffeee0 in ?? () #2 0x817c5f7 in x_event_to_emacs_event (x_event=0xbffff2c8, emacs_event=0x874dc14) at event-Xt.c:991 #3 0x817e0a5 in emacs_Xt_event_handler (wid=0x8457128, closure=0x0, event=0xbffff2c8, continue_to_dispatch=0xbffff20f "\001") at event-Xt.c:2429 #4 0x4021b0f2 in ?? () from /usr/X11R6/lib/libXt.so.6 #5 0x4021b9fd in ?? () from /usr/X11R6/lib/libXt.so.6 #6 0x4021bc2d in ?? () from /usr/X11R6/lib/libXt.so.6 #7 0x40225ce9 in ?? () from /usr/X11R6/lib/libXt.so.6 #8 0x817d3ad in emacs_Xt_next_event (emacs_event=0x85a6140) at event-Xt.c:2381 #9 0x80e2a5f in event_stream_next_event (event=0x85a6140) at event-stream.c:568 #10 0x80e3d49 in next_event_internal (target_event={gu = {type = Lisp_Type_Record, val = 35035216}, s = {bits = 0, val = 70070432}, u = {bits = 0, val = 70070432}, ui = 140140864, i = 140140864, v = 0x85a6140, cv = 0x85a6140}, allow_queued=1) at event-stream.c:2022 #11 0x80e4141 in Fnext_event (event={gu = {type = Lisp_Type_Record, val = 35035216}, s = {bits = 0, val = 70070432}, u = {bits = 0, val = 70070432}, ui = 140140864, i = 140140864, v = 0x85a6140, cv = 0x85a6140}, prompt={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}) at event-stream.c:2239 #12 0x8094908 in Fcommand_loop_1 () at cmdloop.c:570 #13 0x8094b19 in command_loop_1 (dummy={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}) at cmdloop.c:494 #14 0x80b5d5a in condition_case_1 (handlers={gu = {type = Lisp_Type_Record, val = 34323189}, s = {bits = 0, val = 68646378}, u = {bits = 0, val = 68646378}, ui = 137292756, i = 137292756, v = 0x82eebd4, cv = 0x82eebd4}, bfun=0x8094af8 <command_loop_1>, barg={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}, hfun=0x8094ba8 <cmd_error>, harg={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}) at eval.c:1653 #15 0x8094ccd in command_loop_2 (dummy={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}) at cmdloop.c:256 #16 0x80b5bf0 in internal_catch (tag={gu = {type = Lisp_Type_Record, val = 34341831}, s = {bits = 0, val = 68683662}, u = {bits = 0, val = 68683662}, ui = 137367324, i = 137367324, v = 0x8300f1c, cv = 0x8300f1c}, func=0x8094c90 <command_loop_2>, arg={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}, threw=0x0) at eval.c:1328 #17 0x80945eb in initial_command_loop (load_me={gu = {type = Lisp_Type_Record, val = 34323161}, s = {bits = 0, val = 68646322}, u = {bits = 0, val = 68646322}, ui = 137292644, i = 137292644, v = 0x82eeb64, cv = 0x82eeb64}) at cmdloop.c:305 #18 0x80abded in xemacs_21_0_i586_pc_linux (argc=1, argv=0xbffff8bc, envp=0xbffff8c4, restart=0) at emacs.c:1705 #19 0x80ad6e5 in main (argc=1, argv=0xbffff8bc, envp=0xbffff8c4) at emacs.c:2122 -- Glynn Clements <glynn(a)sensei.co.uk&gt;