This problem is one that must be frustrating! Every day the Debian exim4 package will mail you the contents of
/var/log/exim4/paniclog if that file is non-empty.
This is done because it is assumed that if there is anything logged there mail is utterly broken, and you need to see it. However in this case the logfile you've quoted shows that the error is not a fatal one:
What this means is that exim tried to talk to
spamd, which is the client provided by spamassassin, and this failed - with the error "connection refused", which implies that
spamd wasn't running, or was otherwise not accepting the connection.
The net result of this is that an incoming message which should have been tested for spam wasn't.
To fix this problem I suspect you want to run:
service spamassassin stop
service spamassassin start
(I've broken that into two steps, because sometimes "
restart" will fail if the service isn't already running - and that's frustrating for all involved.)
I hope that helps, but if not I'd suggest you drop us a mail to our support address, and we'll try to fix it for you.