java.lang.IllegalArgumentException: View not attached to window manager

[Amab]

java.lang.IllegalArgumentException: View not attached to window manager
at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:672)
at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:368)
at android.view.WindowManagerImpl$CompatModeWrapper.removeView(WindowManagerImpl.java:160)
at android.app.Dialog.dismissDialog(Dialog.java:319)
at android.app.Dialog.dismiss(Dialog.java:302)
at es.ugr.swad.swadroid.modules.Messages.postConnect(Messages.java:264)
at es.ugr.swad.swadroid.modules.Module$Connect.onPostExecute(Module.java:469)
at es.ugr.swad.swadroid.modules.Module$Connect.onPostExecute(Module.java:1)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4921)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)
at dalvik.system.NativeStart.main(Native Method)