When trying to save an existing user, an error message appears which says:
This email is already being used by "Name (firstname.lastname@example.org)", please use a different email.
- Vend for Mac or PC
The reason that this user cannot be saved is that an email address has been entered which is already in use by another user.
If you have a password manager this may be automatically filling in an existing email when you try to save your changes. In this instance temporarily disabling your password manager should resolve this issue.