Error in Connectors - Cases->Custom Object

I am trying to map from the Salesforce Cases object to an object I created “Product Feedback”

I have account & case ID both mapped and used as identifiers, but every time I try and save I get the error:

Please map the mandatory field(s) "SFDC Case ID,Account" and also set them as identifier(s).

Is there something else I am missing about mapping to customer objects? Does this need to go through Rules instead?

Thanks!