Hi Arun,
Quick question:
1. When the event is reported, have you seen any value in MODIFY DURATION field /SAPTRX/EH_EXPEV. If yes then go to 2, otherwise if you don't have any value in duration. It won't pass the data in the alert.
2. The event management parameters for event message EM attribute ID "EE MODIFY DURATION" not assigned to EV, it may be the problem. I have explained long back how to configure in this link EM BAPI I couldn't find any SAP OSS note too to solve this issue. Can you raise SAP OSS message and see what is the outcome from SAP?
Regards
GGOPII