Program failure (67) of " formail -rtzc -xTo: >tmp.from"

I notice in my Smartlist log following error:

------------------ Tue Nov 28 10:03:55 CST 2006
procmail: Program failure (67) of " formail -rtzc -xTo: >tmp.from"
To: <[email protected]>
Subject: Delivery Status
--------------
(it should record but "From: " line is missing)

I checked and this recipe is only in "rc.request" and "rc.submit".
File permissions on related files are:

-rw-rw----   1 smlst   smlst     577 Dec  2 09:31 tmp.from
-rw-rw----   1 smlst   smlst    7571 Dec  2 08:36 tmp.mail
-rw-rw----   1 smlst   smlst    9816 Dec  2 09:31 tmp.request

The occurances of this error are almost all from mail daemon bounces
(only a small portion of all mail daemon mails).  Other than this the 
smartlist is working fine.

I googled but don't find much on this (what's the code "67" for?)

Zhiliang