Between different versions of Carbonite, the assigned user select buttons change as an added feature for more functionality . After upgrading, they need to be reassigned.
You can find instructions to reassign user select buttons with the following links:
V5/15 using Dashboard - http://help.rossvideo.com/carbonite-02/Tasks/Setup/Personality/UserButtons.html
Pre V12 - only Aux and CC buttons were assignable, so button 1 is Aux 1
>V12.3/1 - Key selects now assignable; button 1 is key select 1
V15/5 - All buttons are now assignable; button 1 is the self key