turning on Session Collaboration requires a TWO-STEP approach:
First, enable Sessiuon Collaboration GLOBALLY. In QMC, go to System->Setup->QlikView Servers->Server name->Documents->Server and mark the next-to-last check box called "Allow Session Collaboration"
Next, enable Session Collaboration INDIVIDUALLY for each document you want to share. In QMC (No publisher), go to Documents->User documents->document name->Availability and check the last check box called "Session Collaboration". See Mike's post for a screenshot.
Only those documents with a marked check box will get the extra menu bar item.