Custom Keymappings Not Staying

[Darkfyre24]

So, I've been wondering about this. I use Ventrilo at the same time as playing the game and my keybind for Vent is Mouse button 4. I've used this for a couple years now and I don't really want to change my vent keybind because the keymapping changes I make don't stick.

Is there anyway I can make it so whenever I login my changes to the keymappings stay instead of me having to change them every time I login? They revert back to the default keymappings after I completely exit the game.