When create a new account and click register go to a 500 error page

[lipes]

i've got a problem in registration... i am testing a creation of a new user and when i hit register button... without clicking in the check box "I agree terms of service" the page jumps to a 500 Error page ...

then in the Browser i've clicked to go back and i've recieved the msg that the user as been created and that the data will be sent by e-mail.
I confirm that i recieved the test email (it's working)

But the problem it's the 500 error page... and the System creates/accept a new user without He/She agreed that check box of the Terms of service ...