Parallels Premium Outgoing Antispam not working

[Dirk Rauber]

Parallels Premium Outgoing Spam on CentOS 6 is not working for me. The maillog shows:

Jul 30 14:50:31 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:50:45 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:50:45 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:51:37 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:51:37 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:51:49 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:51:49 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:52:04 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:52:04 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:52:06 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:52:06 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088
Jul 30 14:52:18 ma23151 ct-milter[43229]: mlfi_eom: ctasd_outbound is on and connect IP in mynetworks list -> working in outbound mode.
Jul 30 14:52:18 ma23151 ct-milter[43229]: ctASd: unknown HTTP error with 127.0.0.1:8088

There are no entries about scanned mails.

I've restarted the service multiple times and also added this to my /etc/hosts:

103.5.198.210 resolver1.plesk.ctmail.com
84.39.152.31 resolver2.plesk.ctmail.com
84.39.153.31 resolver3.plesk.ctmail.com
38.113.116.210 resolver4.plesk.ctmail.com
64.191.223.35 resolver5.plesk.ctmail.com

, as suggested in http://kb.parallels.com/de/115257 . There are no firewall rules active and netstat tells me the service should be reachable:

tcp        0      0 127.0.0.1:8088              0.0.0.0:*                   LISTEN      43262/./ctasd.bin

Any suggestions what I could try?