KB15152: 'Unknown error (Unknown message 0) - Error in Process method of component' error occurs when trying to display the elements of an attribute in a prompt window or in the Object Browser in MicroStrategy Developer

SYMPTOM:
A user gets the following error when trying to display the attribute elements of a particular attribute on a prompt or in the Object Browser in Strategy Developer:
 

 
SQLEngine got an Exception from DFC : Unknown error (Unknown message 0)
Error in Process method of component: SQLEngineServer, Project Revenue, job 1616, Error Code= -2147212800
CAUSE:
One or more attribute forms in the attribute definition are empty, as shown below:
 

 
ACTION:
Delete the empty attribute forms or populate them with a valid expression.