amavisd-new not using clamd

[Tom Munro Glass]

I have installed ClamAv and amavisd-new to work with Postfix. They are mostly 
working except that when I start amavisd I get the following message in 
maillog:

Found secondary av scanner Clam Antivirus - clamscan 
at /usr/local/bin/clamscan

When a message is sent to amavisd for scanning I get the following message:

WARN: all primary virus scanners failed, considering backups

I have checked that /usr/local/etc/clamav.conf and /usr/local/etc/amavisd.conf 
are both referring to the same socket file in /var/run/clamav/clamd. I am 
running both clamd and amavisd as user vscan so I don't understand why 
amavisd isn't using clamd.

Any ideas?

Regards

Tom Munro Glass