The GN4 application pool must be set to "integrated mode" in the version 2.1.

Integrated mode handles all requests through a unified pipeline for IIS and is tightly integrated with ASP.NET through that same pipeline.

ASP.NET sees every relevant request and manipulates things along the way rather than acting as an external plugin.

With integrated mode ASP.NET runs much more efficiently in IIS and will yield greater performance for your site.

Warning: currently GNPortal needs "Forms authentication" enabled but client apps need it disabled. Please create two different web apps to use both of them. No problems for I4.