The file element needs a special file decorator, which is added by default. When you set your own decorators for file elements, you delete the default decorators. For example :
$element->setDecorators(array(
array('ViewHelper'),
array('Errors')
));
You should use a File decorator instead of the ViewHelper for the file element, as shown below :
$element->setDecorators(array(
array('File'),
array('Errors')
));​
