What version of Lightroom?
Note that if it is Lightroom v6 you will need to unzip the file (.lrcat) from the "....lrcat.zip" file before opening in LR 6.
I have the same problem with LR5.
I have installed in the past this license on two computers, one mac and one pc.
The I got a new LR6 license and I have installed it on the two computers. I have disinstalled LR5 from both.
Now I would like to use the LR5 license on another pc, but when using the license number (24 digit), it says that this license is alredy in use.
What I should do?
THis is not the same problem (the problem in the original post was catalog wouldn't open) and you'd be much better off putting it in it's own thread.