Lesson learned. Don’t name your partial views the same as your normal views.

Login.cshtml under Views/Shared
Login.cshtml under Views/Login tries to call Html.RenderPartial(“Login”)

Stackoverflow Exception because the rendering engine ends up searching the Views/Shared after everything else and ends up recursively calling Views/Login/Login.cshtml.

Renaming the shared View to _Login.cshtml obviously fixed the issue.

Partial Views explained:
http://bradwilson.typepad.com/blog/2008/08/partial-renderi.html