So a project that I am currently a part of is using an ASP.NET 2.0 HttpModule to add some additional values to the incoming HTTP request's headers in the DEV environment (i.e., our local disconnected laptops) to simulate what an enterprise single-sign-on solution is performing in the production environment. It has worked like a charm. That is until I installed the new security update for the .NET Framework 2.0 release this past Wednesday, July 10, MS KB928365.
Apparently this "hack" has been disabled with the release of this security update.
When attempting to call Headers.Add(), with or without the above hack in place, you will now receive a PlatformNotSupported exception.
All in all, this post is by no means a rant against the security update, but simply an attempt to add a quick answer to the "Google answer machine" for those searching. I am also already aware of a number of other potentially better solutions than the one currently in place for simulating those user accounts, but for now, simply uninstalling the above referenced security update gets the team back working again.