javaScript and ASP.NET

[Eruggesee]

I'm having a hard time getting my head around some of the changes in ASP.NET.<BR>In my Classic ASP app I have a series of image buttons. When a user clicked on a button I used a javaScript function to change the image src to a "selected" image and then set a hidden variable in my form using "document.frmMap.mapTool.value = http://aspmessageboard.com/archive/index.php/'whatever'". Later, when the form was submitted, I used this value to dictate what action was performed. However, now that I've added a couple of web controls to my .aspx page, and "runat=server" to the FORM tag this no longer works - it generates a runtime error saying that "document.frmMap.mapTool.value" is null or not an object . I'm a little mystified. Can anyone point out what I'm doing wrong.<BR><BR>Thanks<BR><BR>masmith