Ok, so I have commented out this line from the sql scheme:
%prefix%phrases ADD INDEX
phrase ) ;
Now it says that the database tables were created successfully :), but now when I create a new user (name, email and password), I try to sign in with my credentials but it says that "You have entered wrong e-mail or password".
Then I checked up the database table iu4_users, to find out that it's empty. So, I guess that my user was never stored. Any ideas?