Xref lisp on close reactor

I am not in any way great with lisp routine programming and or Reactors.

My issue:

I want all xrefs to be changed to relative paths upon close of drawing.

I have a lisp routine that will change all paths to relative but when I insert this reactor below into acad2007doc.lsp I get the following error..

; error: Exception occurred: 0xC0000005 (Access Violation)

here is the reactor:

(defun AtEndCommand (calling-reactor b)
(if (= (nth 0 b) "CLOSE")
 (my lisp routine)
)
)

(defun loadTheReactor ()
(vl-load-com)
(if *FileOnClose* (vlr-remove *FileOnClose*))
(setq *FileOnClose*
(vlr-command-reactor nil '((:vlr-commandEnded . AtEndCommand)))
)
)
(loadTheReactor)

Any help would be greatly appreciated