Symptoms

After a user submitted a form to start a workflow, the approver would open the form and see the following error: SmartObject property GUID is required for property select method Read. Value must be set.

 

Diagnoses 
The SmartObject GUID is used to populate the Approval state of the form. That GUID was empty.
 
 

Resolution 
We saved the GUID as a parameter on the form level and passed the parameter to the SMO.