I am currently using Lightromm CC 2015.2.1. After using it for a while it freezes up. I am on Windows 7 PRO, i5 w/ 16GB. THe catalog is only 4000 images. The problem has occurred a number of time. But lately it has been when I am applying keywords to images. There is nothing else going on in the system (< 2% usage for everything else). Once I kill the lightroom process tree, I can restart Lightroom and it will work again for some time before it happens again. This issue only started with this point release of Lightroom, version 6.0 and 6.1 did not seem to have these issues. Thank you for your help.
I did both things you suggested. Still hung up and I had to kill the Lightroom process tree. I could not even stop Lightroom by clicking on the "Windows X button" on title bar.