Same problem as describe here :
http://shoutbox.menthix.net/showthread.php?tid=25747
Apparently, Messenger Plus! only works if under Administrators account. If you want it to work under every type of account, you have to reset the permissions on the messenger plus files (located in Program Files) to default.
To do so you have to (assuming the Messenger Plus! 3 folder hase the right permissions unlike its subfiles/subfolder. In my computer it was the case) :
1. Browse to the "Messenger Plus! 3" program folder. (The default location is "C:\Program Files\Messenger Plus! 3")
2. View the security permission entries for this folder. This can be done
by right-clicking the folder and choosing "Properties". The
permissions can be viewed on the "Security" tab of the folder properties.
If the "Security" tab is not visible, Simple File Sharing is enabled, and
must be disabled before continuing.
3. Click the "Advanced" button on the "Security" tab to open the "Advanced
Security Settings" dialog.
4. On the "Permissions" tab, select the option entitled "Replace permission
entries on all child objects with entries shown here that apply to child
objects", and click "Apply".
5. Click "Yes" in the security dialog warning that all explicitly defined
permissions will be removed from child objects.
6. Click "OK" to close the "Advanced Security Settings dialog.
7. Click "OK" to close the "Properties" dialog box.
