Hrvoje Niksic writes: Not to be difficult, but here is the backtrace again. The command was `recenter', which calls `center-to-window-line'. Anyway, this happens to me for my optimised and debugged version on IRIX, and my optimised version at home on Linux. All of these were non-Mule. The IRIX versions were compiled with SGI's compiler, and Linux with gcc 2.7.2. Here is a sample program that crashes the system. Here is the run log: sag1 $ xemacs --version XEmacs 21.0 "Finnish Landrace" [Lucid] (mips-sgi-irix6.4) of Tue Aug 25 1998 on sag1 sag1 $ xemacs -vanilla -l ~/crash.el -f do-crash Fatal error: assertion failed, file /sag1/u4/sag1_dev4/craffert/xemacs/xemacs-21.0-b54/src/redisplay.c, line 6757, cur_elt >= 0 Fatal error (6). Your files have been auto-saved. Use `M-x recover-session' to recover them. Please report this bug by running the send-pr script included with XEmacs, or selecting `Send Bug Report' from the help menu. As a last resort send ordinary email to `crashes(a)xemacs.org'. *MAKE SURE* to include the information in the command M-x describe-installation. If at all possible, *please* try to obtain a C stack backtrace; it will help us immensely in determining what went wrong. To do this, locate the core file that was produced as a result of this crash (it's usually called `core' and is located in the directory in which you started the editor, or maybe in your home directory), and type gdb /ms/user/c/craffert/exec/xemacs core then type `where' when the debugger prompt comes up. (If you don't have GDB on your system, you might have DBX, or XDB, or SDB. A similar procedure should work for all of these. Ask your system administrator if you need more help.) Lisp backtrace follows: center-to-window-line(nil nil) # bind (window n) recenter() do-crash() # bind (arg) command-line-do-funcall("-f") # bind (dir file-count line end-of-options first-file-buffer file-p arg tem) command-line-1() # bind (command-line-args-left) command-line() # (unwind-protect ...) normal-top-level() # (condition-case ... . error) # (catch top-level ...) Abort sag1 $ -- Colin