Hai,

I am using Infragistics V10.1. I have a tab control in my report preview form. One report have more than 1 sub reports. I am generating the sub reports and placing it in a seperate tab pages in runtime. 

I have to remove this tab page on click of close button in tab. And also If i have only one tabpage i have to change the tab style as Wizard. So i write the coding as below to remove the tab and to change the style in the "TabClosed" event.

Private Sub uchildtabctrl_TabClosed(ByVal sender As Object, ByVal e As Infragistics.Win.UltraWinTabControl.TabClosedEventArgs) Handles uchildtabctrl.TabClosed
        Try
            If e.Tab.TabControl.Tabs IsNot Nothing Then
                e.Tab.TabControl.ActiveTab = Nothing
                If e.Tab.TabControl.Tabs.Count = 2 Then
                    e.Tab.TabControl.Style = UltraTabControlStyle.Wizard
                End If
                If e.Tab.TabControl IsNot Nothing Then
                    e.Tab.TabControl.Tabs.Remove(e.Tab)
                End If
            End If
        Catch ex As Exception
            QbShowError(ex)
        End Try
    End Sub

But i got "Unhandled error" sometimes. I attached the video for your reference. I also placed the "Innerexception" text below.

System.NullReferenceException was unhandled
  Message="Object reference not set to an instance of an object."
  Source="Infragistics2.Win.UltraWinTabControl.v10.1"
  StackTrace:
       at Infragistics.Win.UltraWinTabControl.UltraTabPageControl.set_Visible(Boolean value)
       at Infragistics.Win.UltraWinTabControl.UltraTabControlBase.OnManagerSelectedTabItemChanged(Object sender, SelectedTabItemChangedEventArgs e)
       at Infragistics.Win.UltraWinTabs.TabManager.set_SelectedTabItem(ITabItem value)
       at Infragistics.Win.UltraWinTabs.TabManager.AutoSelectTab(ITabItem tab)
       at Infragistics.Win.UltraWinTabs.TabItemUIElement.OnTimerTick(Object sender, EventArgs e)
       at System.Windows.Forms.Timer.OnTick(EventArgs e)
       at System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(ApplicationContext context)
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
       at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
       at InstantUI.My.MyApplication.Main(String[] Args)
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException:

Note : I got error only when i set the tab control's "Autoselect" as true. If i set it as false, this error didnt come (please refer the inner exception above). I have no coding for the tab control other than this "TabClosed".