RC 6: You are attempting to take a private survey

Hello,
I have updated CS yesterday to the 3.5.9 version and als the cjlib is updated.
I don't know if it cam from the update but since then I get the next announcement when trying to fill in a survey:

RC 6: You are attempting to take a private survey without a valid key. Please survey creator/administrator for help.

The links are send by the acymailing plugin in a welcome newsletter for a subscription.
Has anyone a Idea how I can resolve this problem?

Thanks in advance
Pjotter