I'm having the same problem too. I previously had a working version 4.5 installed on Windows Server 2003, ASP.NET 2.0. No problems. Today, I tried upgrading to version 4.8 using the "install" download, not the "upgrade". Copied all of the files, made changes to web.config, and ran the install page. Upgrade succeeded with no errors reported, but when trying to access my site in Firefox, I get the same error messages as others (endless redirect) and my IIS logs show multiple 302 errors.
There are multiple posts in the forums with the same or similar problems (I have tried to list a couple I have found below).
http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/107/threadid/202131/scope/posts/threadpage/1/Default.aspx
http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/111/threadid/200731/scope/posts/Default.aspx
I don't think it is a problem with my version of ASP.NET 2.0 since I had DNN 4.5 working on my server with no problem (unless somehow something has changed in version 4.8 which has not been published). This post has suggested fiddling with the .NET trust level settings (changing to Full trust, using medium trust, commenting out the entire trust section). I have experimented with each of these, and none help. The second post above suggests it may be an error with ASP.NET Ajax. I have the same version of System.Web.Extensions registered in the web.config file as I previously had, so it is not a versioning issue. Is it possibly something else with Ajax?
Has anybody figured out what the specific problem is or problems are (i.e., if it is a trust level issue, which module/dll requires the Full trust level)? If so, how to solve it? Anything more specific than a general "changing the trust level" would be helpful in further troubleshooting.
Thanks.