This error happens after a migration to EPiServer CMS 5 r2 when you try to change the password of a user or possibly create a user. The error is very missleading and has nothing to do at all with the role nor membershipprovider. The error is actually a very simple one.

Another user is using the email that you are providing or your user does not have an email at the moment.

All you need to do is either delete one of the users or change the mail adress of one of the users in order to ”lock them up” and be able to change the password.