It may either be this plugin and if not, the only other plugin I can think of that may be causing this is the user hint plugin....However, I'll start here:

It seems that this issue only regards to the admin.

Users who go to the forums, and profiles from the menu bar are unable to click the "Send Message" button that appears on the user hint for only the main admin.  With everyone else it works okay...They see the "Send Message" in the user hint, but once they click it for the admin, nothing happens when a message box should appear at the bottom...