wp-login.php?action=register redirects to wp-signup.php

Hi,
I have a wp 3.0.1 with network enabled.
I was trying to customize the register page with Register Plus Redux.
The problem is that the plugin is customising the wp-login.php?action=register page but when i try to go there I’m redirected to wp-signup.php page.
I tried the plugin in another 3.0.4 installation (without network) and works prefectly.
Any idea?
Ciao,
Paolo