Symptoms
Client had a form that was operational an hour prior to this error. Now when opening the form the Smart Object Methods in the rules have disappeared and show this error "The SmartObject SQL_SO_ProjectIntakeRequest_ProjectUser or one of its components could not be resolved. Error Details: Value cannot be null. Parameter name: s"
Diagnoses
The SQL server was not responding
Resolution
Client refreshed the SQL Server Service - which fixed the problem