If you encounter the error: "Unable to Open Catalog", find the catalog package in Finder. Right-click on the catalog package and select Get Info from the context menu.
In the Get Info window, uncheck the Locked property.
The catalog should now open properly.
Alternatively, right-click on the .cocatalog file and select Show Package Contents from the list. Then delete writelock file there.
Navigate to your catalog folder in the Explorer. Check the Properties of the catalog package by pressing right-click -> Properties -> Read-only (make sure there is no checkmark next to this option).
Alternatively, go to the Catalog folder in the Explorer and delete writelock file there.