The current version of this plugin only supports Joomla 3.3.1 (and Joomla 2.5)
DO NOT INSTALL ON JOOMLA 3.2.0 ! Joomla 3.2.0 currently saves the last successful password upon automatically. That is not compatible with the plugin (for obvious reasons).
Please note: this plugin can allow an admin to masquerade as another user which is a recipe for abuse. Hopefully only ethical admins will install it.