I recently installed Lightroom CC 2015 6.1 on my computer, but when I start the start the software I get a dialog with the message "Lightroom catalog cannot be opened because another application already has it opened.". I have installed and used it in the past but have never got this error before.
Have you checked on Google? This was the first result:
Solution: Delete the catalog lock file
To resolve this issue, do the following:
Close the Lightroom application. Go to the folder where your catalog file [yourcatalogname].lrcat is saved. By default, Lightroom saves catalogs in the following folders:
- Windows: \Users[user name]\Pictures\Lightroom
- Mac OS: /Users/[user name]/Pictures/Lightroom
Move the [yourcatalogname].lrcat.lock file to the Trash (Mac OS) or Recycle Bin (Windows), if it is present at this folder location.
Caution: Do not delete or move the main [yourcatalogname].lrcat file.
Relaunch Lightroom. If your catalog opens successfully, you can empty the Trash (Mac OS) or Recycle Bin (Windows).
When a program opens a file (such as your catalog) it often locks the file so other programs can't modify the file while the first program is using it.
If the program crashes before unlocking the file the file is basically in an orphaned locked state. The easiest way to unlock the file is to restart your computer.
There are various programs that can unlock a file, but it's sketchy if you don't know what you're doing.