EditText setError no funciona en PopupWindow

Tuve popup window con diseño personalizado que tiene edittext . Estoy intentando mostrar el mensaje de error en edittext con método del setError , pero está dando la excepción siguiente.

 android.view.WindowManager$BadTokenException: Unable to add window -- token android.view.ViewRootImpl$W@211ffd68 is not valid; is your activity running? at android.view.ViewRootImpl.setView(ViewRootImpl.java:579) at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:282) at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85) at android.widget.PopupWindow.invokePopup(PopupWindow.java:1104) at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:1008) at android.widget.PopupWindow.showAsDropDown(PopupWindow.java:968) at android.widget.Editor.showError(Editor.java:334) at android.widget.Editor.setError(Editor.java:355) at android.widget.TextView.setError(TextView.java:4654) at android.widget.TextView.setError(TextView.java:4639) at com.ebusiness.worldofjobs.helpers.HelperEditText.isEmailValid(HelperEditText.java:38) at com.ebusiness.worldofjobs.activities.LoginActivity$4$2.onClick(LoginActivity.java:149) at android.view.View.performClick(View.java:4785) at android.view.View$PerformClick.run(View.java:19884) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5343) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700)

Ventana emergente:

 View popupView = LayoutInflater.from(LoginActivity.this).inflate(R.layout.popup_reset_password, null); EdiText etSmaple = (EditText) popupView.findViewById(R.id.etSmample); Button buttonSample = (Button) popupView.findViewById(R.id.buttonSample); final PopupWindow popupWindow = new PopupWindow(popupView, 600, 400); popupWindow.setFocusable(true); buttonSample.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // Here's the exception raising etSample.setError("Nothing..."); } }); popupWindow.showAtLocation(popupView, Gravity.CENTER, 0, 0);