when opening a catalog, LR4 gets hung up and takes 5 minutes to open or stays hung up and i have to force quit and sometimes i have to reboot my Mac. Also atleast 50% of the time or more when I am importing a session the boxes are gray and don't show the images but show up in Bridge. I have to quit LR4 then reopen LR4 to see the images. Lastly, many times when trying to import from my card reader, I click on the reader and no images show or nothing happens at all. I have to quit LR and reopen one or more times before I see the images to import. All These things have not happened when on my PC Windows 7. I am now on a Mac El Capitan. Thanks for your help.