I encountered the same problem. Can't login yaf in version 2.0.0. This yaf instance has been integrated to Umbraco. I need to log in Umbraco back office first then I can log in yaf. Does any one know what happened?
Following is the error message I got from event log.
Exception System.NullReferenceException: Object reference not set to an instance of an object. at PMS.Core.EventHandler.Member.Member_AfterSave(Member sender, SaveEventArgs e) at umbraco.cms.businesslogic.member.Member.SaveEventHandler.Invoke(Member sender, SaveEventArgs e) at umbraco.cms.businesslogic.member.Member.FireAfterSave(SaveEventArgs e) at umbraco.cms.businesslogic.member.Member.Save() at umbraco.providers.members.UmbracoMembershipProvider.ValidateUser(String username, String password) at YAF.Pages.login.GetValidUsername(String username, String password) at YAF.Pages.login.Login1_Authenticate(Object sender, AuthenticateEventArgs e) at System.Web.UI.WebControls.Login.OnAuthenticate(AuthenticateEventArgs e) at System.Web.UI.WebControls.Login.AttemptLogin() at System.Web.UI.WebControls.Login.OnBubbleEvent(Object source, EventArgs e) at System.Web.UI.Control.RaiseBubbleEvent(Object source, EventArgs args) at System.Web.UI.WebControls.Button.OnCommand(CommandEventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)