so i downgraded from el capitan to yosemite and i cant seem to open my photo library

So i have a macbook air early 2014 model and i downgraded from el capitan to yosemite. i manually backed up my files onto a external hard drive and i moved all my files back to yosemite. but i cant seem to open my photo library. when it tries to repair, it says it cannot open library. the photos are really important so if anyone can help me out it would be great. thanks in advance.