Command can throw two TYPES of exceptions:

ECApplicationException: This exception is thrown; if the error is RELATED to USER input and it always fail. When the user ENTERS invalid parameter, this exception is always thrown. When this exception is thrown, the solution controller does not retry the command, even if the command is specified as retriable. 

ECSystemException: This exception is thrown if a runtime exception or any WebSphere configuration error occurs. Examples of this exception are Remote Exception, Create Exception or other EJB exceptions. When this exception is thrown, the solution controller retries the command if the command is retriable and the exception was caused by either a DATABASE dead lock or database rollback.

Command can throw two types of exceptions:

ECApplicationException: This exception is thrown; if the error is related to user input and it always fail. When the user enters invalid parameter, this exception is always thrown. When this exception is thrown, the solution controller does not retry the command, even if the command is specified as retriable. 

ECSystemException: This exception is thrown if a runtime exception or any WebSphere configuration error occurs. Examples of this exception are Remote Exception, Create Exception or other EJB exceptions. When this exception is thrown, the solution controller retries the command if the command is retriable and the exception was caused by either a database dead lock or database rollback.