I did the update this morning from LR 5.4 to 5.7. Everything seemed to be functioning fine. I had to reboot, doing a Windows update, now I come back on, go to open LR5.7, it tells me the catalog is in use, that I need to close it before I can open with this application, yet, this is a fresh restart, nothing should be using the catalog?
I only have the one catalog, and its not large, I should be able to access it.
Open the folder containing your Lightroom catalog and look for a file with the .lock extension. You need to delete that file, then Lightroom will start again for you.
Thank you Jim.