Unable to generate keys to encrypt backup !!

Hi

I'm a little lost on how to use the encryption keys for backup but if I understood well, it works this way:

-> generate backup key on each server I want to backup. -> create scheduled backup (will it use automatically key created ? as I see nothing in backup schedule page to select encryption key !!).

So how do you generate keys successfully ?? On one server it tells me email has already been used to generate a key but it's not listed :( On the other one I get an error: Failed to create backup key : Key generation failed : .+++++ +++++

Does it work really ? and if so how ? as help didn't give me enough details to sort it out !!

Thanks

Vincèn