After an update yesterday I can't open Lightroom. A box appears to say that Lightroom catalog is open in another application (which it isn't) and that's as far as I can get. Does anyone have any useful suggestions?
You may try few things to fix this issue.
1. Close all the application, restart the machine.
2. Reset Lightroom preferences, refer: Preference file and other file locations | Lightroom CC and 6
Open the folder that contains your 'Lightroom catalog' and check whether there is a file with 'lrcat.lock' extension. If it exists then delete same and try relaunching Lightroom.