It sounds like you are not dragging your Workout Blender application to the trash before you try to install the updated version. Could you verify that you are using the process outlined in this thread at the beginning for updating the Mac version? (Copied below) If you are doing this and it still is giving the error, please let me know and we will go from there. Thanks!
After the new installer file downloads from our web site, double click on the disc image (the file called Install_Workout_Blender_Mac_094b.dmg) to mount the installer disc. Next, and this is important or the update will not work, you must open your "Applications" folder, scroll down to "Workout Blender", and drag the application into the trash can. Next, go back to the Workout Blender installer, click on Install Workout Blender and follow the directions. When you launch the Workout Blender, all of your existing imported videos and workouts will still be there.
Curtis W. Kapus
C A T H E D O T C O M
626 Delsea Drive North
Glassboro, NJ 08028