User/Group conflict: "Some email addresses are already used."
User/Alias conflict: "Email address 'firstname.lastname@example.org' is already used."
The email address is already being used by an existing User account. The same name cannot be used again for Group, Alias, Mailing List, or Resource name. Kerio Connect creates a separate folder in the directory structure; that is why it reports a User/Group conflict.
Use another name for Group, Alias, etc. Click the Details button to see the location where the name was created initially.