Workflow Error: Ax2012 : Failed to find execution event handler class for automated task

Hi guys 

I am developing a workflow on ax2012, when i submit my workflow, it works fine, and workflow is submitted to workflow engine and status is changed to submitted, later the workflow does not proceed further and i checked the workflow history it shows me below error: 

 Stopped (error): X++ Exception: Failed to find execution event handler class for automated task "AXWCustCarApprovalEventHandler" (it is my class name for approval event)

 at SysWorkflowHelper-createInstance

SysWorkflowWorkItem-invokeWorkItemEventHandler

SysWorkflowWorkItem-raiseWorkItemEvent

SysWorkflowWorkItem-createWorkItems

SysWorkflow-save

SysWorkflowQueue-resume