Hi,
Seems to be strange. When I checked the same scenario in EHP 4, I was able to revoke the entry sheet. Anyway, you may check the below option:
Please go to PO - service tab and change the service quantity to 1840. Now, go to ML81N and try to revoke the entry sheet. Once its reversed, again go to the PO and change the quantity back to original quantity. If its still giving error, you may check for SAP notes (I couldnt find anything relevant) or raise an OSS ticket to SAP.
In order to avoid this kind of issues in future, you may maintain the message SE 363 as error (E) message.
Regards,
AKPT