I didn't know of your Providers infratructure, but I am sure it have anything to do with the configuration.  Perhaps it is a issue with the configuration of the Server on your Providers site.  I have done several installs, on Windows 2008, 2008R2 and 2012 with SQL Server 2008SP2 /2008R2 without any problems.

I know some Providers needs Special configurations, and sometimes it can be havy to come around what happens.  But a 404 issue looks like a configuration and mostly a permission issue.

Definitify, DNN 7.0.x still running on SQL Server 2005, DNN 7.1.x need SQL Server 2008 SP2 or higher.  The database could still running on SQL Server 2005 mode if it was not migrated to 2008 or higher.  You can check it via SQL Management Studio on the database settings.   One other Change is that 7.1 have Major changes to the jQuery and jQueryUI and is delivered with new libary Versions.  If a custom Skin loads it's own jQuery this can have issues with the DNN 7.1.x Version!

It could also be that the Provider or an Windows Upgrade have add some Settings to the web.config file, that not compatible with DNN.  E.G the WIF (Windows Identity Framework) can make some issues if it is or was installed on the Server.  But the WIF issue Looks others as yours.  So I am on a stand that I have no idea what it can be, it will be hard to found it out w/o Access to the Server.