Unfortunately, this is a post mortem report. Switching buffers using the tabs was ok after startup. But after a while when selecting one of the tabs - boom. In XEmacs 21.2 (beta33) "Melpomene" [Lucid] (i686-pc-linux) of Tue May 2 2000 on altmark configured using `configure --site-includes=/usr/local/include --site-libraries=/usr/local/lib --cflags=-O3 --debug=no --error-checking=none' Lisp backtrace: # bind (print-message-label) display-error((error "illegal callback" Memory fault (core dumped) C stack backtrace doesn't give that much: altmark＠altmark: altmark (3) $ gdb /usr/local/bin/xemacs core GNU gdb 4.18 Copyright 1998 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-suse-linux"... Core was generated by `xemacs -l .emacs -l .xemacs-initial-load.el'. Program terminated with signal 11, Segmentation fault. warning: wrong size gregset struct in core file warning: wrong size fpregset struct in core file Reading symbols from /usr/X11R6/lib/libXaw.so.6...done. Reading symbols from /usr/lib/libtiff.so.3...done. Reading symbols from /usr/lib/libpng.so.2...done. Reading symbols from /usr/lib/libjpeg.so.62...done. Reading symbols from /usr/lib/libz.so.1...done. Reading symbols from /usr/X11R6/lib/libXpm.so.4...done. Reading symbols from /usr/X11R6/lib/libXmu.so.6...done. Reading symbols from /usr/X11R6/lib/libXt.so.6...done. Reading symbols from /usr/X11R6/lib/libXext.so.6...done. Reading symbols from /usr/X11R6/lib/libX11.so.6...done. Reading symbols from /usr/X11R6/lib/libSM.so.6...done. Reading symbols from /usr/X11R6/lib/libICE.so.6...done. Reading symbols from /lib/libdl.so.2...done. Reading symbols from /lib/libdb.so.3...done. Reading symbols from /usr/lib/libgdbm.so.2...done. Reading symbols from /usr/lib/libgpm.so.1...done. Reading symbols from /lib/libncurses.so.5...done. Reading symbols from /usr/lib/libesd.so.0...done. Reading symbols from /usr/lib/libaudiofile.so.0...done. Reading symbols from /lib/libm.so.6...done. Reading symbols from /lib/libc.so.6...done. Reading symbols from /lib/ld-linux.so.2...done. Reading symbols from /lib/libncurses.so.4...done. Reading symbols from /lib/libnss_files.so.2...done. Reading symbols from /lib/libnss_dns.so.2...done. Reading symbols from /lib/libresolv.so.2...done. warning: wrong size gregset struct in core file warning: wrong size fpregset struct in core file #0 0x0 in ?? () (gdb) where #0 0x0 in ?? () I will start XEmacs from within gdb and see if this gives more information. Markus