File's format too new for this application
I am trying to use FCP6, which I just installed, on my new MacBook Air. I have been editing in FCP6 for years on my iMac, and there are some projects I'd like to work on while I'm on the road, so I got a new MacBook for that purpose. From the iMac, I was using an external drive to capture the footage and the fcp file is also on the external drive. But when I hooked up the external drive to the new MacBook Air, I get the warning that "the file's format is too new to use with this application". How do I solve this? For what it's worth, the iMac is still on Mavericks, but the MacBook Air is on Yosemite. Does that make a difference?
MacBook Air, OS X Yosemite (10.10.3)