By definition I had to post this question. I received the error on this line using ASP.NET MVC 3 and ASPX form. Where’s my typo?
<a href="<%= Html.Action("About", "Home") %>">
<img src="<%= Url.Content("~/Content/images/newfront_04.jpg") %>" /></a>

I created a blank project to compare:
- Web Config is identical minus connection strings (including Views web.config)
- Global.asax.cs including routes is identical minus namespace
- Page directive is identical
- Home Controller code is identical minus namespace
- Taking this line out makes everything work
- The entire page is html with the exception of the page directive and ContentPlaceHolders
- This is the Site.Master file
Html.Action is actually rendering that action where you are putting that code, and it’s causing reentrancy there. That is: it’s calling the whole action and outputting the resulting view… not outputting the url.
What you probably wanted was Html.ActionLink (which renders the whole A tag for you), instead, or Url.Action, to just output the URL – rather than the action result again.