I am having the same issue. My issue instead was I went from an iMac to a Macbook Pro using a Time Machine back up. Same and latest Motion 5 on both. No available updates in the app store.
When I try to open up my files on the Macbook Pro I get that same message.
However, over at www.motionvfx.com in their FAQ section there is this:
[MOTION] When I try running one of your projects, Motion tells me that I need version 5.2 or 5.5. This version doesn't exist yet, what gives?
Apple uses two XML tags to describe a project's version - "ozml version" and "displayversion". Even though the latter one is always correct (5.0.2, 5.0.6, 5.0.7 etc), Motion reads the ozml version (5.2, 5.5) when checking the required build. Because of this it "thinks" that you need Motion 5.5 instead of 5.0.7 (for example). The solution is easy - simply update Motion to the latest build via App Store (the updates are free) and everything will be fine.
Anyone know of a fix to that response? There is no update by the way.