interactive "r" argument passing

Dear w32 emacs gurus:

Why does this function not work? I think that similar functions I wrote 
long ago did work.:


(defun save-sscratch (start end) ;; M-x sch alias
"Append region in *scratch* to file scratch.txt"
(interactive "r")
(with-current-buffer "*scratch*"
    (append-to-file start end "c:\mydocu~1\scratch.txt")))

Do I need escaped backslashes? forward slashes?


Thanks,

Ed