EMAIL input doesn`t work in HTML 5 form

I have a very simple FORM, but for some reason it doesn`t post the input properly to the action PHP site. When I push the submit button, the debiteuren.php starts downloading with an error in????

<form role="form" action="debiteuren.php" method="POST">

<input class="form-control" type="email" name="customer_email" >  

<button type="submit" class="btn btn-default" name="customer_form" value="button">Opslaan</button>