This usually means it has features of a version you don't have, since you have Developer, it most likely uses 2.5+ features.
If someone made this file for you, you may need that the person remove or replaces anything 2.5+ exclusive to make it compatible.
Although, the other possibility is that it uses features from the current beta version, so if it interests you, you can update to that for free.
I've been using the beta for ages, and the latest version is pretty stable. Contains loads of great new features, too.