[exim] Problem since upgrading spamassassin

Hello,

Yesterday, i upgraded SpamAssassin from "3.0.3-2sarge1" to
"3.1.7-1~bpo.1" on a Debian Sarge box, using the following repository:

============================================================
deb http://www.backports.org/debian sarge-backports main contrib non-free
============================================================

However, since the upgrade, around 50% of the messages have been
bouncing with the following message:

============================================================
421 SMTP incoming data timeout - message abandoned
============================================================

Having investigated a little further, we are seeing lots of messages
like these:

============================================================
mail:/var/log/exim4# grep BSMTP /var/log/exim4/mainlog.1
2007-02-27 17:10:34 1HM5le-0008Sj-5j <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 17:23:09 1HM5xn-00009Z-Cn <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 17:33:14 1HM67a-0000GO-BB <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 17:51:29 1HM6PC-0000UI-Kl <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:02:01 1HM6ZN-0000aK-JK <user2@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:14:39 1HM6lf-0000hq-4x <user3@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:31:31 1HM71z-0000rC-Qm <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:42:12 1HM7CJ-0000xC-Ss <user4@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:42:14 1HM7CM-0000xN-HD <user1@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
2007-02-27 18:42:19 1HM7CR-0000xX-4h <user2@???>:
sa_spamcheck transport output: An error was detected while processing a
file of BSMTP input.
============================================================

Do you know what is happening here? Do i need to adjust some config due
to the upgrade?

My current exim config (which worked fine with "3.0.3-2sarge1") is as
follows:

Router:
============================================================
sa_router:
   no_verify
   check_local_user
   # When to scan a message :
   # - it isn't already flagged as spam from Spamassassin
   # - it isn't already scanned
   # - it isn't local
   # - it isn't from one internal domain user to another
   condition = "${if and { \
                         {!eq {$received_protocol}{spam-scanned}} \
                         {!eq {$received_protocol}{local}} \
                         {!eq {$sender_address_domain}{$domain}} \
                         } \
                         {1}{0}}"
   driver    = accept
   transport = sa_spamcheck
   local_parts = /etc/spamassassinUsers
============================================================

Transport:
============================================================
sa_spamcheck:
driver = pipe
command = /usr/sbin/exim4 -oMr spam-scanned -bS
use_bsmtp = true
transport_filter = /usr/bin/spamc
home_directory = "/tmp"
current_directory = "/tmp"
user = spamcheck
group = spamcheck
log_output = true
return_fail_output = true
return_path_add = false
message_prefix =
message_suffix =
============================================================

Thanks in advance for any advice,
Richard.

-- 
Richard Hobbs (Systems Administrator)
Toshiba Research Europe Ltd. - Speech Technology Group
Email: richard.hobbs@???
Web: http://www.toshiba-europe.com/research/
Tel: +44 1223 376964        Mobile: +44 7811 803377