Well, since you are using the clamav scanner, you should add the line
deb http://volatile.debian.net/debian-volatile etch/volatile main
to your sources.lst. Volatile is for packages which may changing in the
etch stable cycle but updates are needed or the package won't work as
expected anymore. Examples are whois, tzdata or the virus scanner clamav.
It may be, that clamav found itself too old to work properly. Some
updates of the virus database require a new scanning engine. Whatever it
is you should found messages in /var/log, clamav.log or mail.log.
Shade and sweet water!
Stephan