Just today I started having trouble with my Lightroom crop tool. It will bring up a crop box in the dimension I specify but I cannot move or change the size of the crop box. It's just kind of frozen there. My system info is below. In case it relates to this, I also posted a problem I've been having for a while, regarding the develop module getting stuck on one photo. Something seems out of wack with my develop module! Can't change to a new photo in Develop Module
This is the version I'm on:
Lightroom version: CC 2015.8 [ 1099473 ]
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.12 
As the crop tool is not functioning properly, please make sure you update Lightroom to version 2015.10.1
Thank you Sahil. I truly thought I was up to date on my versions, as I tried to update quite recently. But I think the update was stopped for some reason and I must not have resumed it. It seems to have solved the cropping tool issue.
Glad it worked out for you Lisa, feel free to reach out to us for any future queries.