KB15399: ‘Error(s) occurred while loading report: DSSSQLEngine: converting Report :Unknown error. (Unknown message 0)...Project XXX, Job XXX, Error Code= -2147212797’ error occurs during report execution in MicroStrategy Developer 10.x

SYMPTOM:
When executing a report, execution fails with the following error in Strategy Developer 10.x:
 

 
Error: Error(s) occurred while loading report: DSSSQLEngine: converting Report :Unknown error. (Unknown message 0) Error in Process method of Component: SQLEngineServer, Project XXX, Job XXX, Error Code= -2147212797' is received.
STEPS TO REPRODUCE:
Follow the steps below to reproduce this issue in the Strategy Tutorial project:
 

• Create a compound metric that looks as follows:
  

•  
  Note that a function does not precede the metric definition.
   
  
• Place the newly created metric on a report containing any attribute.
• Execute the report, and the error message will be received.

CAUSE:
The metric editor validated an expression that was not valid.
 
ACTION:
In order to resolve the issue, either place a function such as 'Sum' in front of the metric definition or delete the '{~}' that follows the metric definition to make the metric automatically sum.