Pro Application Support 4.0.2 PROBLEM INSTALLING

I have a copy of Logic Pro and when i try to start the program i get an error message that reads:"This version of logic Pro requires Pro Application Support 4.0(687.0) or newer Prokit 591.0".....So i went to the apple site and found the download for Pro Application Support 4.0.2 and when i went to install that
I am taken to the installer BUT when i choose the destination to install this on (my HD) there is a red exclaimation point on the HD icon and when i click on it i get this message:"You cannot Install Pro Application Support on this volume.This volume is not eligible for this update". WHAT IS THE PROBLEM HERE? WHY CANT I INSTALL THIS???