How do I figure out which ASP control is throwing an exception?
<p>I am getting the following exception from my ASP page during rendering:</p>

<p>Cannot have multiple items selected in a DropDownList.</p>

<p>at System.Web.UI.WebControls.DropDownList.VerifyMultiSelect()
   at System.Web.UI.WebControls.ListControl.RenderContents(HtmlTextWriter writer)
   at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.Control.Render(HtmlTextWriter writer)
   at System.Web.UI.Page.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)</p>

<p>None of my code is in the stack trace, and my page has seven drop down lists on it. I am setting the selected rows on the drop down lists in my code based on data from several database tables as well as rules about default selections. So it is quite possible I have a bug where I set the selected item on one of my fields.  But how can I tell which field is causing the problem?</p>

<p>In Global.asax I have</p>

<pre>
    void Application_Error(object sender, EventArgs e) 
    {
        // Code that runs when an unhandled error occurs
        Exception lastException = Server.GetLastError();
    }
</pre>

<p>Which I am able to set a breakpoint on but nothing in the exception seems to tell me which field was being rendered when the exception got thrown.</p>

<p>Any hints on where to find this information or debugging strategies that will help me find it?</p>
