[Exim] spam acl condition: cannot parse spamd output

I have some logging information for a problem that seems to have persisted on some new hardware ...

2003-10-08 15:26:46 <message ID> spam acl condition: cannot parse spamd output
2003-10-08 15:26:46 <message ID> H=<external host name> (<external host name>) [<external host IP>] Warning: ACL "warn" statement skipped: condition test deferred:
2003-10-08 15:40:22 <message ID> spam acl condition: cannot parse spamd output
2003-10-08 15:40:22 <message ID> <= <> H=<external host name> (<external host name>) [<external host IP>] P=esmtp S=1512749 id=<external mail ID>@<external host name> T="Delivery Status Notification (Failure)"
2003-10-08 15:40:23 <message ID> => <local user>@<local mail server> <<local user>@<local mail server>> F=<> R=deliver_smtp T=smtp H=<local mail server name> [<local mail server ID>]
2003-10-08 15:40:23 <message ID> Completed

Does this look like and exim/exiscan/SpamAssassin problem?

It has been suggested that I don't spam score larger messages, but I'd like to spam score every inbound email ... and this one isn't that big!!
Not every email that develops this problem is a delivery failure, but they all exhibit similar behaviour.
The emails seem to be delivered okay, but I'm not happy with these messages appearing in the panic log.

Any help would be very much appreciated,

Alex