Do not upgrade to the latest version, and if you have, then downgrade immediately. Unfortunately, there is a bug that was introduced with this new version:
On the new message page, the drop down user list does not include admins (and maybe other roles as well). I got loads of reports from the users not being able to contact a few users, and I noticed that the users that were excluded from the list were admins. I have not yet checked yet if other roles (like Editor) is excluded.
Nonetheless, I would highly suggest that people downgrade to the earlier version if you are relying on this plugin as means of communication between admins and users.