Update Problem
Unable to update Motion 5.1.2 to the latest (5.2.1)...
App store tells me I already have Motion installed and should refer to the update function.
Uh...it never shows up in my updates.
MacBook Pro (Retina, Mid 2012), iOS 6.1.4
Try this knowledge base article:
Final Cut Pro X, Motion 5, Compressor 4: Issues updating via the Mac App Store - Apple Support
Also make sure you don't have copies of the app on other connected partitions when you try your update. Eject other drives that may have copies of motion before trying to update. If you need to keep old copies refer to the knowledge base article, it talks about how to properly make back-ups if you need them.