There are a couple of things you could probably try.
If you have a previous version loaded on your computer (say 5.0.1) you could try what omeone else recently noted, trashing Motion and re-installing.
You can also try contacting the app store support since they are probablly best equipt to help with purchase problems.
Make sure your computer is logged in to the App Store/iTunes. Launch either and go to the Store menu. There's a log in/log out option there. Verify it is logged in.
Exactly what are you seeing?
When you say Lakeside, is that the New Orleans store? If so, email me (it is in my profile), we have a local FCP users group.