Android Question android.app.FragmentManagerImpl.moveToState java.lang.IllegalArgumentException

Exception java.lang.IllegalArgumentException:
  at android.app.FragmentManagerImpl.moveToState (FragmentManager.java:1297)
  at android.app.FragmentManagerImpl.addAddedFragments (FragmentManager.java:2431)
  at android.app.FragmentManagerImpl.executeOpsTogether (FragmentManager.java:2210)
  at android.app.FragmentManagerImpl.removeRedundantOperationsAndExecute (FragmentManager.java:2166)
  at android.app.FragmentManagerImpl.execPendingActions (FragmentManager.java:2067)
  at android.app.FragmentManagerImpl$1.run (FragmentManager.java:742)
  at android.os.Handler.handleCallback (Handler.java:958)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loopOnce (Looper.java:230)
  at android.os.Looper.loop (Looper.java:319)
  at android.app.ActivityThread.main (ActivityThread.java:8919)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:578)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1103)

Sub SafeShowPage(PageID As String)
    ' Always delay the page switch to make sure the Activity and fragments are ready
    CallSubDelayed2(Me, "InternalShowPage", PageID)
End Sub

Private Sub InternalShowPage(PageID As String)
    If B4XPages.GetPage(PageID) <> Null Then
        B4XPages.ShowPage(PageID)
    Else
        Log("Page " & PageID & " does not exist.")
    End If
End Sub