Recipe works, but gives error message

I have the following recipe which is intended to trap messages longer than 75k, 
trash
them, and send back a canned response:

:0 c
* > 75000
* !^FROM_DAEMON
| (formail -r -A"Precedence: junk" \
   -A"X-Loop: fischman(_at_)nynexst(_dot_)com" \
   -i"From: postmaster(_at_)miata(_dot_)net" \
   -a"From: postmaster(_at_)miata(_dot_)net" \
   cat $MAILDIR/bigfile.msg)| $SENDMAIL -t

        :0 Ah
        $DEFAULT


The operation seems to work as intended. It deletes the incoming message and 
sends back
the response file. But in the log file, I get the following error followed by 
the normal
log entry:

USER: Undefined variable.
procmail: Error while writing to " (formail -r -A"Precedence: junk" \
   -A"X-Loop: fischman(_at_)nynexst(_dot_)com" \
   -i"From: postmaster(_at_)miata(_dot_)net" \
   -a"From: postmaster(_at_)miata(_dot_)net" ; \
   cat $MAILDIR/bigfile.msg)| $SENDMAIL -t"



What might be causing this? Thanks for any help.

-- 
Gary J. Fischman                
NYNEX Science & Technology Center