Problem solved. It was due to the fact I removed the certificate manually (something that should be allowed since this is a conffile!). I reinstalled the certificate by purging maemosec-certman-common-ca and reinstalling it (together with as-daemon-0, which was removed at the same time).
cmcli -c common-ca -r 8868bfe08e35c43b386b62f7283b8481c80cd74d
cmcli -T common-ca -L | grep DigiNotar