New Photos, External Hard Drive Library wont show, Permissions

I downloaded the new update, which included the latest Photos update. I have been using iPhotos as my main photo viewing application for my photos and videos, with my library being stored on my external hard drive (Shown on hard drive as "iPhoto Library"). When I control click the Photos application and choose the library from my external hard drive, it loads to about 8% before giving the warning "Photos was unable to make a copy of your library before preparing it. Photos does not have the necessary permissions...". I have tried running the sudo commands that I am directed to (If Photos can’t copy or create a library - Apple Support), which hasn't worked; I have a sneaking suspicion that it only works when the iPhotos library is under the Pictures folder on the main hard drive. I have no idea what to do to get Photos to recognize or access my HD's library. I've even gone so far as copying the Master's folder to try and use Lightroom, but it is not so great with videos. Can anyone help? Thank you!!