If the built-in repair routines can't fix the catalog, I don't believe there is anything you can do. You will probably have to revert to your most recent good back up, and start the import process again. As you build this new catalog again you should probably consider backing up more frequently. I wonder if it's possible that one of your CDs was corrupted.
Thank you Jim. I do believe that there were errors on one of the CDs because it contained images that could not be read. I am rebuilding the catalogue from the most recent backup; but it will be a lot of work.
Computers are great, until they're not.
I went back to my most recent backup with the intent to parse my large database into component catalogs and add from there so instead of one very large catalog (or about 80K pictures), I would have two catalogs of 40K each. However, when I went back to my most recent backup (having 55K images) as my starting point, I found the following: This version ran well; but when I tried to back it up, the optimization routine ran continuously for over 7-hours. The Windows Task Master showed that LR4 was still running, even after 7-hours. I suspect something is wrong with this backup version and I could go back to the previous backup version (since this one obviously backed up properly, it might be a better starting point to parse build up my database. Would upgrading to LR5 help? Presumably LR5 has better repair functions than LR4 (one might hope). Maybe I need to get paid help from Adobe to proceed in my repairs so I don't inadvertently make matters worse.