Error at "antispam" start.

[cezar]

Good afternoon!
I had an important question. After "antispam" start there is a hard error. The email server works normally, except for sending and obtaining of letters to users. The email server is in a local area network in firm. After the sending, all messages get to mail queue. The waiting reason: «host 127.0.0.1 [127.0.0.1] said: 451 4.5.0 error inprocessing, id=30641-031, virus, scan failed: virus_scan: no virus scanners avaible (in reply to end of data command)». Reboot of an email server doesn't give result even after "antispam" switch-off. Mail sending starts to work only after computer reboot on which the email server is installed.
Somebody can will prompt a cause of error?
1 id=30174-05, id=28043-10 etc., at each message the id.