I'm using the Adobe Audition beta for mac. I don't know what I did wrong, all was working great and sudently, I can't open anymore a song in the wave form to edit it. When I try to go to the waveform there is a popup in the middle that says "Multitrack session not active. Mixer controls are enabled only when a multitrack session is the active document". So, whats that? How to fix that and return to normal??
It sounds like you may have closed the Editor panel that contains your active document. Go to the Window menu in Audition and choose "Editor" to open the panel and bring it to the front. The Mixer panel is only used when you have a Multitrack session open as the active document so this text is just informing you of that.