yann.fr wrote: Not ok because

"This e-mail is already registered. If you forgot your password, click on the <strong>Forgot your password</strong> link and a new password will be sent to you."

Only the first part of the sentence seems appropriate.

You can of course modify the massage as you feel suites you.

I believe that the reason it is worded like this is for the following case:

A user has forgotten his username/password and tries to create a new account with the same email address as before.

So the message has 2 meanings - email address is in use and if the email address is yours, then perhaps you need to request a username/password reminder.