I have backed up my LR catalog on 2 seperate drives, after backing up, I have tried to open each one of the back ups, however, I get a pop up on each of them that says - Lightroom cannot use the catalog named "name of catalog" because it is not writable and cannot be opened.
I just went through the process of restoring a backup the other day. I extracted the catalog from the zip file and then copied that catalog to the folder where the damaged catalog was. Then I double clicked on the catalog and LrC opened normally. I could have started LrC in the normal fashion as well. Did you do something similar to what I did?