Grid not showing proper output . .

Hello everyone . .

I am new to Dynamics Ax 2009 .

Actually the problem faced by me is that i have a combobox and a grid on a form and when i select any entity of the combobox ,say any Vendor Id ,i get the proper result of the fields required by me but after that succesively when i select any other element from the combobox,i get the previous result as well as the new result both appended . .

Please give me some immediate and effective solution for this . .

Thanks . .