Since upgrade to 3.8.1 login box from Network theme, doesn't work

Before the upgrade to 3.8.1, when login in from the login box at the top of the network theme, It worked.

Now when you login you are taken to wp-login.php the error message is ERROR: Cookies are blocked or not supported by your browser. You must enable cookies to use WordPress.

You can login fine from here.

Any ideas how to get that working again?

Thanks,

Matt