iFrame parser error after upgrading to .NET 4.5

Question

We have recently upgraded all of our WebForms projects to .NET 4.5, and encountered a parser issue when loading pages with an iFrame element. We have corrected

Answer 1

Further (or in as a combination of the answers here).

I don't believe it's needed to actually change the tags from iframe to asp:HtmlIFrame if you have the reference to the updated System.Web.UI.HtmlControls.

I updated my web.config to remove specific versions of the tag prefix and replace it with:

Clean and rebuild the project and that regenerates all the designer tags for me with the correct HtmlIFrame output.