An error occurred during the processing of . Only Content controls are allowed directly in a content page that contains Content controls.

I got this strange error when modifying the page under SharePoint library, i bit little confused when this error happens. For a couple of minutes i look the code and tags, then i found out i missed runat=”server” in asp:content tag. After adding runat=”server” to asp:content tag, now the page works fine.

Note: If you are using Server side code within this type of pages, mention runat=”server” within <script> tag.
ie., <script runat=”server”></script>
If you are misssed that, the same error will happens.