This would mean the invite failed at the getNotification function. Please ensure the invite has a Subject AND Body, both are required by CB API. Currently CB Invites allows either/or, but that is not appropriate and will be fixed for next release to force subject and body. Usually having a prefix of some kind resolves missing subject and a header or footer of some kind would resolve missing body.

Thanks for your answer.
The invite has ALL, Header, Suject Prefix,Body and Footer.

Does the invite fail for ALL email addresses or just a specific one? It's failing at the CB mailer function.

Furthermore, I don't know why the Prefix, Header and Footer are displayed. It's confusing the user

It's displayed so the user understands how the email will be formatted exactly.

Yes for ALL email addresses. All other emails are working fine (GJ invites, CB Mass Mail, CB workflow mails, CB notification mails, etc)

Don't see how that's possible. It uses the exact same function as GJ for example to send emails. Only thing I can think of is the email address is being distorted during the save process perhaps. Please PM me a test email address that is failing. Perhaps something in the address could be cause it to fail or something in the subject/body perhaps. I'm not able to duplicate your issue locally.

I understand what you mean but do you think an user will understand all these codes like, Registration - www.singlesenergy.com/index.php?option=c...sters&Itemid=510
tonta - www.singlesenergy.com/index.php?option=c...er=45&Itemid=510
...or will it see it as a kind of bug?

Not a bug; it's displaying as designed. You're welcome to edit the template files of CB Invites however.

Have also just noticed that, as in CB Blog plugin, even if in the configuration a limit has been set to 5, the CB Invites overview page still displays "Limit: unlimited" (test made from a simple registered page)

This is a known bug.