Unable to create FTP account or change password. Plesk does not show any error, but the process does not finish.
The problem is caused by large amount of files locating under document root of domain. This behavior has been confirmed as a software issue #PPP-4613 .
According to Release Notes for Plesk 12 for Windows the speed of creating FTP accounts and performing other operations on files was increased for subscriptions that contain large numbers of files. Please consider upgrading your Plesk to the latest version.