Signing In fails before checkout In virtuemart

I'm using Virtumart on Joomla.

Here is my problem : After adding some products to the cart, when I choose to checkout, I have two solutions (as any usual E-commerce website) :

1. Signing up
2. Signing in

I'm having some troubles with the second one. When I fill all the fields and validate the form. it redirects me to the same page but loaded with a different template instead of the checkout page.

BUT when I deactivate the Javascript, it works...

here's a link to a product for testing.

The only Javascript that seems to be pointing at my form is the function submitregistr开发者_如何学Pythonation Feel free to check if other functions do.