[EXTREMELY URGENT] All email addresses rejected during registration

[brendonhatcher]

Hi

Joomla 2.5.4, VM 2.0.6

I had the site on a development url, did extensive testing.
Moved the site to the live URL (on the same server).

Now, when users try to register (using any of the virtuemart registration screens (i.e. at any stage of checkout), they are told to "Please enter a valid Email address."
This warning appears after they submit the registration form and are redirected back to the shopping cart.

The email address is valid, and even occurs if I use email addresses that I used during the test phase (I deleted all the test users, so it is not a clash with already registered users).

Any ideas?

Thanks
Brendon