va01 enhancement

Hi ,

in va01 transaction second screen i am entering sold-to-party value

then i am entering meterial number in line item without pressing the enter button again i am going beck to the sold-to-party i am changing the value which i entered previously

now i am pressing the enter button i am getting the popup information window

instead of displaying the popup information window i need to show the error message

could u explain how to do modifications where i have to make changes.