Errors not showing correctly

I am using GF on a bookshop site and users can send an email to the store to see if the book is available. When you click for more info a window appears with data prepopulated from the product info and you should be able to send the form.

http://hetgoedeboek.be/boekens/dagboekbijbel/

click "informatie vragen"

The issue is... if you don´t put an email, even though it´s required the form disappears when you click send. ONLY if you click the link to send the email again do you see that the form did not send and the email field needs to be sent as well.

What can I do so this doesn´t happen and you see the field error right away. I am using AJAX in the popup window too?

Thanks!

Definitely making progress. I think this has helped me so the form doesn´t send but my required fields don´t show what needs to be changed. Like how it highlights them...

For example. click the "vragen" link here and leave out email: http://hetgoedeboek.be/boekens/dagboekbijbel/

Appreciate the help.