The Controls Collection Cannot Be Modified
This issue happens in the following situation.
When there is having code blocks like <%= ... %> on aspx page and
We are trying to append controls dynamically from code behind.
For example, on the following figure, there is having code blocks on head section.
From code behind, we are appending one link to the header section.
For resolving this issue, we have to modify the code block section as shown in the figure.
Code block should be <%# ... %> instead of <%= ... %>
By this way we can resolve this issue.