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First, please tell what version of BSD you have.
How much experience do you have with BSD or similar OS.
Is this a new problem that started after some time, or is the a new install and it was like this from the start.
What computer do your have and what mouse are you using. It can make a difference. Not all mice are equal.
Have you tried a different mouse and restarted the boot-up?
Have you already looked in BSD and GNOME documentation for clues? If so, what did you try that did not work.
Have you already read this?
http://ubuntuforums.org/showthread.php?t=665740Yes, it is the Ubuntu forum, but the topic is about GNOME It is a rant about how weak GNOME is or mouse settings.
Here is the relevant link in the GNOME library.
http://library.gnome.org/users/gnome-access-guide/stable/dtconfig-2.html.en