error while cancelling the amount in sales order conditions tab

Hello Experts ,

when I am updating using BDC it works all fine but when I am trying to cancel the amount for the same condition type it says

00 347 S Field KOMV-KSCHL(1) is not an input field

00 347 S Field KOMV-KBETR(1) is not an input field

00 347 S Field RV61A-KOEIN(1) is not an input field

Thanks in advance.