I'm using Joomla 2.5.6 and when I enable EEC it will not let anyone register. It gives the following incorrect warnings:
The name you entered is not valid.
The username you entered is not available. Please pick another username.
The passwords you entered do not match. Please enter your desired password in the password field and confirm your entry by entering it in the confirm password field.
When I disable EEC the registration form works as designed.