Forum Error

System.Web.HttpException (0x80004005): Server cannot append header after HTTP headers have been sent.
   at System.Web.HttpHeaderCollection.SetHeader(String name, String value, Boolean replace)
   at System.Web.HttpHeaderCollection.Set(String name, String value)
   at Microsoft.Owin.Host.SystemWeb.CallHeaders.AspNetResponseHeaders.Set(String key, String[] values) in /_/src/Microsoft.Owin.Host.SystemWeb/CallHeaders/AspNetResponseHeaders.cs:line 107
   at Microsoft.Owin.Host.SystemWeb.CallHeaders.AspNetResponseHeaders.set_Item(String key, String[] value) in /_/src/Microsoft.Owin.Host.SystemWeb/CallHeaders/AspNetResponseHeaders.cs:line 66
   at Microsoft.Owin.Infrastructure.OwinHelpers.SetHeaderUnmodified(IDictionary`2 headers, String key, String[] values) in /_/src/Microsoft.Owin/Infrastructure/OwinHelpers.cs:line 708
   at Microsoft.Owin.Infrastructure.OwinHelpers.AppendHeaderUnmodified(IDictionary`2 headers, String key, String[] values) in /_/src/Microsoft.Owin/Infrastructure/OwinHelpers.cs:line 767
   at Microsoft.Owin.HeaderDictionary.AppendValues(String key, String[] values) in /_/src/Microsoft.Owin/HeaderDictionary.cs:line 157
   at Microsoft.Owin.Infrastructure.ChunkingCookieManager.AppendResponseCookie(IOwinContext context, String key, String value, CookieOptions options) in /_/src/Microsoft.Owin/Infrastructure/ChunkingCookieManager.cs:line 173
   at Microsoft.Owin.Security.Cookies.CookieAuthenticationHandler.<ApplyResponseGrantAsync>d__13.MoveNext() in /_/src/Microsoft.Owin.Security.Cookies/CookieAuthenticationHandler.cs:line 310
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Security.Infrastructure.AuthenticationHandler.<ApplyResponseCoreAsync>d__40.MoveNext() in /_/src/Microsoft.Owin.Security/Infrastructure/AuthenticationHandler.cs:line 178
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Security.Infrastructure.AuthenticationHandler.<ApplyResponseAsync>d__39.MoveNext() in /_/src/Microsoft.Owin.Security/Infrastructure/AuthenticationHandler.cs:line 167
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Security.Infrastructure.AuthenticationHandler.<TeardownAsync>d__34.MoveNext() in /_/src/Microsoft.Owin.Security/Infrastructure/AuthenticationHandler.cs:line 95
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Security.Infrastructure.AuthenticationMiddleware`1.<Invoke>d__5.MoveNext() in /_/src/Microsoft.Owin.Security/Infrastructure/AuthenticationMiddleware.cs:line 32
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContextStage.<RunApp>d__7.MoveNext() in /_/src/Microsoft.Owin.Host.SystemWeb/IntegratedPipeline/IntegratedPipelineContextStage.cs:line 84
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.<DoFinalWork>d__12.MoveNext() in /_/src/Microsoft.Owin.Host.SystemWeb/IntegratedPipeline/IntegratedPipelineContext.cs:line 152
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.StageAsyncResult.End(IAsyncResult ar) in /_/src/Microsoft.Owin.Host.SystemWeb/IntegratedPipeline/StageAsyncResult.cs:line 76
   at Microsoft.Owin.Host.SystemWeb.IntegratedPipeline.IntegratedPipelineContext.EndFinalWork(IAsyncResult ar) in /_/src/Microsoft.Owin.Host.SystemWeb/IntegratedPipeline/IntegratedPipelineContext.cs:line 167
   at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
   at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
   at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)