Base Layout: <input name="event" type="hidden"/>

We are using a struts based framework, with our JSP's being tiled. We were recieveing a "undefined" or null object error when we would click on the headers or do any sort of key-stroke/data entry. We decided to go through out baselayout.jsp which was being extended for our current page. We found that editing baseLayout.jsp and takeing the line <input name="event" type="hidden"/> out from the baselayout caused the error to dissappear. Does anyone know why this causes problems? I'm a little confused as to what this line is actually doing.