Pipe timeout problem with 0.14.3-1

[Laurence]

Hi, I just installed 0.14.3-1 using Debian's dselect.  I'm using exim as my
MTA so my .procmailrc is configured with the default:

:0fw
| bogofilter -u -e -p

# if bogofilter failed, return the mail to the queue, the MTA will
# retry to deliver it later
# 75 is the value for EX_TEMPFAIL in /usr/include/sysexits.h

:0e
{ EXITCODE=75 HOST }

Now all messages get stuck in the queue - they eventually get returned with
"pipe delivery process timed out".

I've looked in all the relevant logs and nothing helpful is logged.

Any suggestions what to try?

Thanks,
Laurence