I got that error when I didn't install the latest version of FP11; restart your browsers/computer before and after installing http://www.adobe.com/support/flashplayer/downloads.html
I believe setup FP 11 correctly following this link: http://priyeshsheth.wordpress.com/2011/10/05/how-to-use-flash-player-1 1-air-3-with-flash-professional-cs5-5/
Is there anything missing? Is there a more official how to setup proscenium and FP11/Air 3.0 guide from Adobe?
OK, after a few weeks coming back to this, and got the ProsceniumTutorials running now, which is fine at the moment, so I'm closing this. Got solved by setting the playerglobal to external, as described here: http://forums.adobe.com/thread/909355?tstart=0