I cannot open my lightroom application. I get a pop up box with the following message:
The lightroom catalog named lightroom 5 cannot be opened because another application already has it open. Quit the other copy of lighroom before trying to launch.
I'm running windows 7, 64 bit
In the folder where the catalog is there is likely a .lock file. Delete this file only then try again.
It is created to prevent Lightroom being used at the same time by more than 1 user, and if Lightroom doesn't shutdown correctly for some reason can remain in the folder.