Update Controller.php

framework/web/Controller.php

@@ -105,7 +105,7 @@ class Controller extends \yii\base\Controller
     public function beforeAction($action)
     {
         if (parent::beforeAction($action)) {
-            if ($this->enableCsrfValidation && Yii::$app->errorHandler->exception === null && !Yii::$app->getRequest()->validateCsrfToken()) {
+            if ($this->enableCsrfValidation && Yii::$app->getErrorHandler()->exception === null && !Yii::$app->getRequest()->validateCsrfToken()) {
                 throw new BadRequestHttpException(Yii::t('yii', 'Unable to verify your data submission.'));
             }
             return true;