将必需的字段验证器限制为一组控件（ASP.NET）

I have a Required field validator attached to a fileupload control. When the user hits the insert button to insert the image into an html editor next to the control the validator fires off if nothing was in the fileupload text box. That works fine; however, when the save button at the bottom of the page is clicked it fires off the required validator if the fileupload control is empty. What i must I do so that validator can only fire off on the click of the insert button?I have a Required field validator attached to a