I\'m in the process of creating a new application and started out using EF6-rc1, Microsoft.AspNet.Identity.Core 1.0.0-rc1, Microsoft.AspNet.Identity.EntityFramework 1.0.0-rc
In my case, running in VS 2013 C#, MVC 5.2.2, using ASP.NET Identity 2.0, the solution was to update the ApplicationUserManager constructor inside App_Start\IdentityConfig.cs like so:
public ApplicationUserManager(IUserStore store)
: base(store)
{
this.UserValidator = new UserValidator(this) { AllowOnlyAlphanumericUserNames = false };
}