ASP.NET "Controls cannot be modified [because it contains code blocks]..." error on one server but not another

Question

I've got a web app that works on my local computer and our test server but is failing in production with this error:

The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).

I've read in a couple places that this can be fixed by changing <%=...%> to <%#...%>, but it intrigues me that the error comes up only in production. What differences in configuration could be causing this?

Complete stack trace (note that it includes the Ajax Toolkit):

System.Web.HttpException: The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
   at System.Web.UI.ControlCollection.Add(Control child)
   at AjaxControlToolkit.ScriptObjectBuilder.RegisterCssReferences(Control control)
   at AjaxControlToolkit.ExtenderControlBase.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Yes. It's actually a module for our CMS system, and it does this when its containing page is loaded. Works fine everywhere else. — Tom Hamming, Jul 07 '11 at 17:38

score 1 · Answer 1 · answered Jan 18 '12 at 22:12

I've come up with something I find a lot easier and more straightforward -- while leaving the tag in the header where it belongs.

First, start the code block with <%# instead of <%= :

<head id="head1" runat="server">
   <title>My Page</title>
   <link href="css/common.css" rel="stylesheet" type="text/css" />
   <script type="text/javascript" src="<%# ResolveUrl("~/javascript/leesUtils.js") %>"></script>
</head>

This changes the code block from a Response.Write code block to a databinding expression. Since <%# ... %> databinding expressions aren't code blocks, the CLR won't complain. Then in the code for the master page, you'd add the following:

protected void Page_Load(object sender, EventArgs e)
   {
      Page.Header.DataBind();    
   }

The DataBind method evaluates all the databinding expression(s) in your header at load time.

score 0 · Answer 2 · answered May 16 '16 at 08:47

wrap your head content where "<%=" used in a placeholder like so:

<asp:PlaceHolder Runat="server">

   <script type="text/javascript" src="<%= ResolveUrl("~/script.js") %>">       

   <link rel="stylesheet" type="text/css" href="<%= ResolveUrl("~/style.css") %>"/>

</asp:PlaceHolder>

score 0 · Answer 3 · answered Jul 07 '11 at 17:20

0

Try to remove <% %> and add your attributes/texts from your code behind

answered Jul 07 '11 at 17:20

Sebastien Robert

331
4
11

I know how the is resolved elsewhere, but given that it works everywhere but production, I'm looking for a reason why it would be different. – Tom Hamming Jul 07 '11 at 17:24

ASP.NET "Controls cannot be modified [because it contains code blocks]..." error on one server but not another

3 Answers3

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