This error message is displayed when the files that ActivManager requires are already in use by another user. The most common reason for this is because there are two users logged onto the same computer (one live user, and another who is logged on, but not currently active). This happens with Fast user switching.
For example, User A logs onto the computer which causes the files used by ActivManager to be loaded and run as system processes. User A then leaves the computer without logging off. User B comes to use the computer, and instead of logging off User A, selects the Switch User option.
User A remains logged in on the computer, but not active, and now User B is logged in too. The files that ActivManager uses to communicate with Promethean devices cannot be reloaded by User B, and because they are already running processes under User A. This causes the error message to be displayed.
To resolve the issue, simply ensure that no other users are logged onto the computer at the same time.