Lisp backtrace follows:

  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  # (unwind-protect ...)
  delete-window(#<window 0x1b73>)
  # bind (next window window)
  window-reduce-to-one(#<window 0x1b89>)
  # bind (combination-start root-window frame)
  frame-reduce-to-one-window(#<x-frame "emacs" 0x1987>)
  # bind (configuration frame)
  really-set-window-configuration(#<x-frame "emacs" 0x1987> [cl-struct-window-configuration #<x-frame "emacs" 0x1987> 444 283 #<buffer " *mouse-read-file*<2>"> 13 10 4 [cl-struct-saved-window nil nil nil nil nil nil nil 0 0 436 262 0 nil nil nil [cl-struct-saved-window nil nil nil nil nil nil nil 0 0 436 221 0 nil nil [cl-struct-saved-window t nil nil #<buffer " *mouse-read-file*"> #<marker in no buffer 0x84d3f1c> #<marker at 1 in  *mouse-read-file* 0x84986bc> #<marker at 1 in  *mouse-read-file* 0x84d3e8c> 0 0
127 221 0 nil nil nil nil [cl-struct-saved-window nil nil nil #<buffer "*Completions*"> #<marker in no buffer 0x84d3f34> #<marker at 1 in *Completions* 0x84986d4> #<marker at 1 in *Completions* 0x84d3e44> 127 0 436 221 0 nil nil nil nil nil]] nil [cl-struct-saved-window nil nil nil #<buffer " *mouse-read-file*<2>"> #<marker in no buffer 0x84d3ff4> #<marker at 1 in  *mouse-read-file*<2> 0x84d400c> #<marker at 1 in  *mouse-read-file*<2> 0x84d3e74> 0 221 436 262 0 nil nil nil nil nil]] [cl-struct-saved-window nil
t nil #<buffer " *Minibuf-0*"> #<marker in no buffer 0x84d3f64> #<marker at 1 in  *Minibuf-0* 0x849856c> #<marker at 1 in  *Minibuf-0* 0x84d3f4c> 0 262 436 275 0 nil nil nil nil nil]]])
  # bind (frame configuration)
  set-window-configuration([cl-struct-window-configuration #<x-frame "emacs" 0x1987> 444 283 #<buffer " *mouse-read-file*<2>"> 13 10 4 [cl-struct-saved-window nil nil nil nil nil nil nil 0 0 436 262 0 nil nil nil [cl-struct-saved-window nil nil nil nil nil nil nil 0 0 436 221 0 nil nil [cl-struct-saved-window t nil nil #<buffer " *mouse-read-file*"> #<marker in no buffer 0x84d3f1c> #<marker at 1 in  *mouse-read-file* 0x84986bc> #<marker at 1 in  *mouse-read-file* 0x84d3e8c> 0 0 127 221 0 nil nil nil nil [cl-struct-saved-window nil nil nil #<buffer "*Completions*"> #<marker in no buffer 0x84d3f34> #<marker at 1 in *Completions* 0x84986d4> #<marker at 1 in *Completions* 0x84d3e44> 127 0 436 221 0 nil nil nil nil nil]] nil [cl-struct-saved-window nil nil nil #<buffer " *mouse-read-file*<2>"> #<marker in no buffer 0x84d3ff4> #<marker at 1 in  *mouse-read-file*<2> 0x84d400c> #<marker at 1 in  *mouse-read-file*<2> 0x84d3e74> 0 221 436 262 0 nil nil nil nil nil]] [cl-struct-saved-window nil t nil #<buffer " *Minibuf-0*"> #<marker in no buffer 0x84d3f64> #<marker at 1 in  *Minibuf-0* 0x849856c> #<marker at 1 in  *Minibuf-0* 0x84d3f4c> 0 262 436 275 0
nil nil nil nil nil]]])
  byte-code("..." [oconfig frame buffer-read-only oframe buffer mconfig buffer-disable-undo nil erase-buffer frame-live-p selected-frame select-frame set-window-configuration] 2)
  # bind (minibuffer-default _history_ oconfig mconfig frame buffer window oframe owindow dir default abbrev-table history readp
keymap initial-contents prompt)
  read-from-minibuffer("Save DTD in: " ("/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced" . 51) #<keymap read-file-name-map size 2 0xf12> nil file-name-history nil "/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced")
  # bind (minibuffer-completion-table minibuffer-completion-predicate minibuffer-completion-confirm last-exact-completion insert
completer initial-contents must-match default dir prompt history)
  read-file-name-2(file-name-history "Save DTD in: " "/home/miken/My_Documents/Clients/PONL/Projects/EOM/" "/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced" nil "Benefits.ced" read-file-name-internal)
  # (unwind-protect ...)
  # bind (user-data dirwin filewin frame butbuf dirbuf filebuf file-p completer initial-contents must-match default dir prompt history)
  mouse-read-file-name-1(file-name-history "Save DTD in: " "/home/miken/My_Documents/Clients/PONL/Projects/EOM/" "/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced" nil "Benefits.ced" read-file-name-internal)
  byte-code("..." [initial-contents must-match default dir prompt history mouse-read-file-name-1 completer] 8)
  # bind (completer initial-contents must-match default dir prompt history type)
  read-file-name-1(file file-name-history "Save DTD in: " "/home/miken/My_Documents/Clients/PONL/Projects/EOM/" "/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced" nil "Benefits.ced" read-file-name-internal)
  # bind (history initial-contents must-match default dir prompt)
  read-file-name("Save DTD in: " "/home/miken/My_Documents/Clients/PONL/Projects/EOM/" "/home/miken/My_Documents/Clients/PONL/Projects/EOM/Benefits.ced" nil "Benefits.ced")
  (list (read-file-name "Save DTD in: " dir tem nil nam))
  # bind (nam dir tem)
  (let* ((tem (expand-file-name (or sgml-default-dtd-file (sgml-default-dtd-file)))) (dir (file-name-directory tem)) (nam (file-name-nondirectory tem))) (list (read-file-name "Save DTD in: " dir tem nil nam)))
  call-interactively(sgml-save-dtd)
  (dispatch-event "[internal]")
  # (condition-case ... . error)
  # (catch top-level ...)

Segmentation fault (core dumped)
[root@camarillo xemacs-21.5.14]#