Is Lightroom completely shut down?
If there is a file in the folder with the lock extension you need to delete that lock file.
LR is shut down.
I cannot see individual files in folder. It just has LRCAT icon and is labeled: LR$ catalog on MacBkPro Previews.lrdata
I see this once in awhile on my Mac with other files where I can not empty a file out of the trash with the same error message. For instance, sometime its when I drag a photo to email to send it to someone and then try to delete and remove the photo from the trash. Its not actually being used but it will not remove from the trash. A COMPLETE restart of the computer is the only way to solve the problem. I don't worry about the trashed files that this happens to until I do a restart. This used to not happen till Yosemite came out and it is still happening in El Capitan. This is another example of the Apple OS quality going downhill fast.
Thank you, Bob. I was able to delete the folder after completely shutting down and restarting computer.
I now have another problem for which I will create a separate post.