I am running Lightroom 5.6 and Mac OS X 10.9.4. I have the Lightroom catalog on my internal drive (279 GB available), and I'm backing up the catalog to an external drive (1.51 TB available.). My image files are on both my internal drive and second external drive. Two days ago, I quit Lightroom and hit the "Back up" button. The "Back Up Catalog" dialog box disappeared, and Lightroom proceeded to check the catalog. I came back the next morning (about 7 hours later), and the "Back Up Catalog" dialog box was on the screen - the same one that I used the night before to initiate the back up. I moved the "Back Up Catalog" dialog box on the screen, and the "Backing Up Catalog" progress bar was revealed; it was behind the "Back Up Catalog" dialog box. The progress bar was animated, so it seemed to be backing up. (My catalog file is about 12.63 GB; my previews file is 3.72 GB; my Smart previews file is 76.7 MB, and there is a file whose extension is "lock" in the same folder as my catalog. The progress bar was about 75% complete. The quit command was greyed out the Lightroom menu, so I brought up "Force Quit Applications" dialog box on my Mac. Although I waited for several minutes, Lightroom was never reported as being "unresponsive". I checked my backup folder on the external drive, and there was a folder named with the date (2014-10-11 1855) and inside of it was lrcat journal file; it was 9 KB. I went ahead and forced Lightroom to quit. When I started it up again, an information box came up that said that because Lightroom quit unexpectedly, it had to examine the catalog. I left for several hours, and when I returned, the information box was gone, and Lightroom appeared to be running fine. When I finished editing a few images, I quit and hit the "Back up" button. The same scenario greeted me this morning. What's happening?