Storyline file won't open in Storyline 360 (It's asking me to upgrade):

Hi there,

We have been provided some Storyline files that we need to edit.  

When we try to open them, we get the following error message:

"This project uses features that are not available in this version of Storyline.  Please upgrade to the latest version in order to open this project."

We are running Articulate Sotryline with the latest Update installed.

I've read that some 360 projects will not be compatible with Storyline 3 however 360 will always open Storyline 3 projects so it should not be that.

I'd be ever so grateful if someone could assist.  Have we missed something obvious here?