Error in proxy logs:
2010:03:31-13:14:05 gatekeeper httpproxy[4820]: id="0003" severity="info" sys="SecureWeb" sub="http" request="(nil)" function="avira_get_instance" file="avirascanner.c" line="175" message="Avira create instance failed (return code 3)"
2010:03:31-13:14:05 gatekeeper httpproxy[4820]: id="0003" severity="info" sys="SecureWeb" sub="http" request="0xb0d015b0" function="avira_scan" file="avirascanner.c" line="329" message="failed to get scanner instance"
Screenshot of error
EDIT: Sorry didn't see it but might be the same as https://community.sophos.com/products/unified-threat-management/astaroorg/f/102/t/69213