Export problem - same mp3 format for each mp3 setting

Hi

I have a problem with my Audition when exporting to mp3.

When I export in different mp3 settings, no matter if it is constant or variable type or it is 320 kbps, 96 kbps, low quality or highest quality, Audition exports the session to the same mp3 format each time. 

Everything is updated both MacBook and Audition. 

Someone who can help me out here?