I have 3 input fields in a pageblocksection, all are required. first field is select list, based on second field is rendered. so, when I select value from select list then an action function is called and the selected value is sent to controller. based on this value section is rerender. then if third field is empty then it gives error. I don't want that error on rerender of section.
sounds more like a sound for apex:actionRegion, which allows you to control what parts of the page should be processed during an AJAX request