Invoice booking with respetc to Service Entry Sheet

Hello Friends

I created one PO (Related to services u2013 Item Category u2018Du2019 and Account Assignment Category u2018Ku2019)

for a Net price of 54,296.35 INR and service entry sheet made for same 54,296.35 INR.

At the time of bill booking through transaction MIRO, I have to book only 52127 INR (After service entry sheet made, vendor offered a special prcie 52127 INR) But in item data (in MIRO) system is not allowing to change Amount to 52127 from 54296.35 INR and throwing following error message.

Condition processing not possible for items with account assignment

Message no. M8575

Diagnosis

This item is subject to account assignment. The system does not allow you to branch to the conditions.

Procedure

To enter or change the amount, branch to the account assignment screen.

P.O. NO.396950 & S/E 1000095526

Could u please explain what would be the problem in this case?

Thanks

Vijayakumar TVN