pmgb on "[Plugin: Theme My Login] No registration"

Hi guys,
it looks like TML is a very good plugin, but I can not make it works. When I try to register, the plugin checks the Username and the E-mail (and the plugin changes the color of the field to green), and then the page stays, it doesn't register the user. The page doesn't say anything more, and no redirection, and it doesn't create a new user.
The short-code I used in my login/registration page:
<div style="float: left;">[theme-my-login default_action='register' show_gravatar="0" show_log_link="0" show_pass_link="0"]</div>
<div style="float: right;">[theme-my-login default_action='login'show_gravatar="0" show_reg_link="0"]</div>
Anybody can help me?
(sorry for my English).

http://wordpress.org/plugins/theme-my-login/