[Exim] using pipe in .forward

I have this at the end of my .forward file:

################################################################################
# The rule to go to the inbox.
################################################################################
if not delivered
then
  #save $home/.mutt/inbox
  #unseen save $home/.mutt/inbox.bak
  pipe "/usr/sbin/exim_lock -retries 1000 $home/.mutt/inbox \
       \"$home/perl/line_breaks $home/.mutt/inbox\""
endif

It sends the mail to the line_breaks script correcly, and that script runs
correctly appending to my inbox. However I get an error mail from
Exim containing the following:
This message was created automatically by mail delivery software (Exim).

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

  pipe to |/usr/sbin/exim_lock -retries 1000 $home/.mutt/inbox
+"$home/perl/line_breaks $home/.mutt/inbox"
    generated by jason@???        

The following text was generated during the delivery attempt:

------ pipe to |/usr/sbin/exim_lock -retries 1000 $home/.mutt/inbox
+"$home/perl/line_breaks $home/.mutt/inbox"



What am I doing wrong here?

Thanks,
Jason