Control contains a block of code (that is, <% ...%>), so the control collection cannot be modified

Error:

Server error in "/" application. the control contains a block of code (that is, <%.%>), so the collection of controls cannot be modified.

Description: An unhandled exception occurred during the execution of the current WEB request. Check the stack trace information For more information about the error and the source of the error in your code.

Exception Details: System.Web.HttpException: The control contains a block of code (that is, <% ...%>), so the control collection cannot be modified.

Source Error:

执行当前 Web 请求期间生成了未经处理的异常。可以使用下面的异常堆栈跟踪信息确定有关异常原因和发生位置的信息。

Stack trace:

[HttpException (0x80004005): The control contains a block of code (that is, <% ...%>), so the control collection cannot be modified. ] System.Web.UI.ControlCollection.Add (Control child) +9871215 System.Web.UI.PageTheme.SetStyleSheet () + 301 System.Web.UI.Page.OnInit (EventArgs e) +9675168 System.Web.UI.Control.InitRecursive (Control NamingContainer) +134 System.Web.UI.Page.ProcessRequestMain (Boolean Includestagesbeforeasyncpoint, Boolean Includestagesafterasyncpoint) +489

Cause analysis: The JS code written in <script> in head contains the <%=...%> code

Workaround: Move <%=...%> find a way into the body (take <%#...%>)

Control contains a block of code (that is, <% ...%>), so the control collection cannot be modified