I have a Guide with a Guide Step Service Call | SalesForce/Free Form Email with Recipient Email address set as a constant and email address entered. How do I fix this error:"Error reason: UNKNOWN_EXCEPTION: Missing refresh token. User might not have been authorized."

I presume this referrs to the Security Token, which I have reset; although this is used for external calles (like Informatica Cloud connection).

Email administration is configured to 
- Send through External Email Service is set to GMail
- Deliverability -  TLS is Required and restricted to smtp.googlemail.com

When I Test Deliverability using my corporate email I do get the 32 test emails. If I use a Gmail account I don't get all 32 test emails. I've tried setting the Step 'recipent email as constant to' my corporate email, a GMail account and as field Current User Email, which is my corporate email. Same error always occurs.