Mapping Hidden field to Salesforce Reference field (i.e. AccountID, Recordtype, ect.)

I keep getting an API error when I try to map a hidden field to a reference field in SFDC. Get message anytime I try to sync hidden field value to AccountID on the contact, or anytime I try to map to a specific recordtype. Any suggestions?

Hi Britni. How are you integrating Gravity Forms and Salesforce? Also, what is the API error you receive?