Hi. There are a couple things we can look at here:
First, if you are using OS X 10.7 Lion, this is the message that you will get upon trying to import video into the Blender. The version currently available for Mac is not compatible with Lion yet.
Second, if you are using an older Mac system (10.6 or 10.5), then you should update Adobe AIR to the current version first to see if that addresses the issue, since the Workout Blender does require a fairly recent version of AIR to work correctly.
And third, while some of the newest series of videos import fine into the older version of the Workout Blender, it is not technically compatible on the Mac with these new videos yet, so there may be a glitch here and there.
On the bright side, we are close to releasing two Mac versions (one for Mac OS X 10.7 and another for 10.6 and 10.5) that will be addressing all of these issues.
Hope this helps.