If I were to make a field compulsory, it displays a grammatically incorrect error message if the field is left empty:
You have error in you from, please fix it!
Since the form is not quite that powerful to detect errors (more of whether or not a field is empty), may I suggest you change it to:
You have left some fields empty, please fill them up.
As a publisher, I find it a little embarrassing to use the form.