Connector MS Dynamics - Could not retrieve the system user "SYSTEM"

I try to connect AX 2012 and CRM 2011, but on Account to Customer Service I get follwing error:

[Account to Customer Service] has encountered an error while processing key [[TestCompanySNI2, d5d3039b-e3fc-e111-abef-00155d012104]]. Could not retrieve the system user "SYSTEM"

I don't know what I have been missing, I tried to make everything like in the install/configuration guide...

Please can someone point me to the right direction!?

Thanks in advance for your help!

br

Stefan