I just updated to the newest version of Lightroom and now my catalog( That i just spent 4 hours working on) in now inaccessible by lightroom. Every time I try to open it, it states that this lightroom catalog is already open in another lightroom and I should close it, but I have no other lightrrom running. I am sure someone has had this problem before and any help here would be tremendous!!
Close LR and open a File manager, Win/File explorer/Computer on Windows or Finder on Mac, and find a file that has a .lock extension and delete it. That .Lock file should be in the same folder as the LR catalog file.