Microsoft recently introduced new ASP.NET Identity - replacement for old (Simple)Membership. Unfortunately, I can\'t use this new membership system in my old project because
I have no idea why this works but it did!
My problem was in VS2013. In the WebConfig, debug was set to true and I got that error. When I set it to false it worked fine and then I reset to true and it continued to work OK!
At first when debug was true before changing to false, I put a break point in my StartUp code and it wasn't reached at all. After changing to false pressing save and then back to true the StartUp code was called and the program works like it should.