Maybe this will help. With the migration to Plesk 10.x and after creating the customers and changing the subscribers to the different domains, I noted it that there was no chance to change the password for some E-Mail Addresses using the GUI, because there was a problem with the Useres associated to the different E-Mail Addresses "Error: The user account was not found. This could happen if the user account was removed by someone else while you were changing its settings.".
I also noted that in some cases the E-Mail Address wasn't associated to any User. In such cases changing the password using the GUI was possible. So my question is: Is there any way to remove the User associated to an E-Mail Address in order to be able to change the password using th GUI?