Hi Sudeesh,
I think there could be a problem within the method that is used by the step. I think this could be probably because of the value or data object that the method s expecting to be available in the method container during run time. I feel like this could be one of the issue.
Secondly, check if there are any secondary methods associated with the step. If existing then make sure the instance of the container element which is used in the methods tab is available at run time.
Thirdly, Check if there are any events which are getting created upon approval action. from SWEL event log.
Finally, make sure you have defined proper binding and while triggering the terminating events make sure you commit the work.
If this is with respect to any of the standard workflow templates , provide us the workflow ID.
Regards,
Pavan