I suspect the problem is caused by something not going right with the MailScanner setup script.
Please do vi /opt/MailScanner/etc/MailScanner.conf and verify everything is set according to my mailscanner.sh script. These are the settings you should be looking for:
%org-name% = orgname
%org-long-name% = longorgname
%web-site% = www.domain.tld
Run As User = postfix
Run As Group = www-data
Incoming Work Group = clamav
Incoming Work Permissions = 0640
Incoming Queue Dir = /var/spool/postfix/hold
Outgoing Queue Dir = /var/spool/postfix/incoming
MTA = postfix
Quarantine User = root
Quarantine Group = www-data
Quarantine Permissions = 0660
Quarantine Whole Message = yes
Virus Scanners = clamd"
Monitors for ClamAV Updates = /var/lib/clamav/*.cld /var/lib/clamav/*.cvd
Clamd Socket = /var/run/clamav/clamd.ctl
Clamd Lock File = /var/run/clamav/clamd.pid
Spam Subject Text = ***SPAM***
Spam Actions = deliver store
Spam Actions High Scoring Spam Actions = store delete
Non Spam Actions = deliver store
SpamAssassin User State Dir = /var/spool/MailScanner/spamassassin
If those are correctly set, then the script works like it should.
ln -s /opt/MailScanner/bin/Quick.Peek /usr/sbin/Quick.Peek
See what you get in your logs now.