Hi,

when clamav is reloading its virus patterns, the daemon control socket vanishes 
for a few seconds. When exim tries to scan a message in this time window, it 
fails and logs a panic entry ("unable to connect to UNIX socket"), which in 
turn triggers all warning mechanisms since panic log entries usually indicate 
fatal conditions. The message is, however, correctly delivered when the remote 
host retries.

Please consider
  (a) trying again after waiting for a few seconds in this case and
  (b) if scanning succeeds on one of the retries log to the main log instead of 
the panic log.

Greetings
Marc