Please follow the below steps :
- Make sure your program is updated to Lightroom 6.3 : Keeping Lightroom Up-to-Date
- Launch Lightroom with Control/Command key pressed and choose Create a New Catalog > Give it a name > try to open it.
- If you are able to open a new catalog, go to File menu> Import from another Catalog > choose your previous catalog to be imported from.
If that does not help, could you please confirm which operating system do you have : Windows or Mac?
I followed all steps, but still it is not working. I am using Windows 8.1.
Error message is that "Lightroom could not import this catalog because of unknown error."
Thanks for your response.
Do you get this second error while importing in the new catalog that you created?
I can create new catalog, but still cannot open my catalog. I opened Lightroom as administrator, still cannot repair the catalog.
This means that the main catalog is corrupted.
I have sent you a PM for further assistance.
Please check that and reply.
Thank you for your help.