I first wrote about a new DotNetNuke redirect loop bug on the 19th of July 2008, about a bug appeared somewhere around version 4.7. Its now February of 2010, the and the latest DotNetNuke 4 version is 4.9.5.
The bug is still there, and still causing redirect loops.
The quickest solution is to open your web.config file and replace every Version=1.0.61025.0 with Version=3.5.0.0 - make sure to get all of them!
The code that causes this is still present in 4.9.5:
If objBasePortalException.Message.Contains ("System.Web.Extensions") Then
' suppress AJAX error in Medium Trust
Response.Redirect(strURL)
This is a terrible mistake that has been pointed out by myself and several others. What this code says is: if the home page has an ajax error then redirect back to the home page.
The problem with this is that the home page will still have the same error! So the error will occur again, and that code will be run again, and it will redirect again, and so on into infinity.
Fortunately the latest version of DotNetNuke 5, 5.2.2 does not have the code above, and the web.config already uses 3.5.0.0. So this particular redirect loop is solved in DotNetNuke 5.
I saw a report of someone having the redirect loop when upgrading from DotNetNuke 4 to DotNetNuke 5. This may have been because the web.config was not automatically updated to use version 3.5.0.0. But I am just guessing now.