simple workflow just run into canceled status, and http 401 error.
i had ruled out the disableloopbackcheck issue.
It turn out that system account is not to allowed to start a workflow now.
RequestorId: 8cf5a232-27b2-bc81-e572-882fe82f742e. Details: System.ApplicationException: HTTP 401 {"Transfer-Encoding":["chunked"],"X-SharePointHealthScore":["0"],"SPRequestGuid":["8cf5a232-27b2-bc81-e572-882fe82f742e"],"request-id":["8cf5a232-27b2-bc81-e572-882fe82f742e"],"X-FRAME-OPTIONS":["SAMEORIGIN"],"MicrosoftSharePointTeamServices":["15.0.0.4420"],"X-Content-Type-Options":["nosniff"],"X-MS-InvokeApp":["1; RequireReadOnly"],"Cache-Control":["max-age=0, private"],"Date":["Thu, 08 Nov 2012 06:44:50 GMT"],"Server":["Microsoft-IIS\/7.5"],"WWW-Authenticate":["NTLM"],"X-AspNet-Version":["4.0.30319"],"X-Powered-By":["ASP.NET"]} The HTTP response content could not be read. 'Error while copying content to a stream.'. at Microsoft.Activities.Hosting.Runtime.Subroutine.SubroutineChild.Execute(CodeActivityContext context) at System.Activities.CodeActivity.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager,