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

Hi all,
I get this error but I just do this in code behind:
The Controls collection cannot be modified because the control contains code blocks (i.e. <% ... %>).
I already tried to put it in a contentplaceholder by replacing "page" by my contentplaceholder "Head"
It is since I used routing and <%= ResolveUrl("css/style_5/style.css")%> to resolve the styling issues.
This is my code:
Dim < ...