Recently, some people have started having problems with VPOP3 Antivirus failing to update (error 52). This is because of some changes on the global update servers.
Please upgrade to VPOP3 Antivirus v1.1.0 (or later)
If that upgrade is not possible, a work around in the meantime is to edit the VPOP3\plugins\vpop3av\vpop3avu.conf file and add the line which says:
DatabaseMirror avupdates.pscs.co.uk
above the line which says:
DatabaseMirror database.clamav.net
You shouldn't need to restart anything, it should pick up the change at the next update attempt.