I was deploying my MVC3 application into a production that did not have the proper DLLs in the GAC. So I used the handy little tool in Visual Studio that allows you to include the DLLs in the BIN folder. Simply right-click on the project in Visual Studio and select Add Deployable Dependencies.
But when I deployed the project into production, it kept attempting to redirect me to Account/Login, which does not exist. And I have not routed those values anywhere.
It turns out that the WebMatrix.Data.dll was copied into my BIN directory and into production. This DLL is the culprit. I removed all instances of this DLL from my project, and the issue went away.