Remove required attribute from a CCK FileField

Question

Hello.

I have a node with a required CCK filefield. I want to remove the field requirement on certain pages, so I added a hook_form_alter in my module and tried the following:

$form['field_image_file']['#required'] = false;

which doesnt work! Printing the $form I see that there are loads of places where the #required value is set to one, for example in the sub-array ['#upload_validators']. Which one is the correct one to set to false? Or should I perhaps use hook_nodeapi instead?

Thanks a bunch,