If you decide you want to rename a Lightroom catalog you can either have it open or closed but when you do rename it you need to rename the lightroom catalog in the finder and the preview file as well at the same time!

If you don’t rename the preview and the catalog at the same time before you launch lightroom again and you just name one of them. The next time you launch lightroom its going to make a new preview file that is blank but your still see all your volumes but all the pictures will be gray, useless, and missing…

You will try and fix this problem by going back trashing the newly created previews and renaming the old one the same name but it will be too late it wont work and you will have to re-import all your images again!

So when your going to rename your catalog rename the previews as well before launching lightroom again and it should work just fine.