file validation problem

I am trying to upload a file and I set the rule bellow,the problem is that even I select a file there is the error Please upload a file.what is wrong,as I notice there is something with validation rule,I have done as this

[['file'], 'file', 'skipOnEmpty' => FALSE,'on'=>'new'],

At controller I set

 $type = new \app\models\Buildobjects();