Hi BillThompson ,
Which version of Lightroom are you using?
Please refer Error: "Unexpected error opening catalog" occurs in Lightroom after Windows 10 upgrade and let us know if that helps.
Also follow the linked steps in the article Recover catalog and images after resetting preferences in Adobe Photoshop Lightroom and let us know if that helps getting your catalog back.
Thanks, Akash, I'm using CC. I did finally fix it by uninstalling LR and reinstalling it.
Thanks for the update.
Glad to know you got it working.
I have just had the "catalog cannot be opened due to unexpected error" issue. So of course I went to a backup--same error. And I have quite a few backup catalogs--same error. And I could not create a new catalog. I fill a large drive in about half a year, so I hauled out the previous one---same thing. I noticed a few days ago a new update of Lightroom had been installed. And I saw the original post for this issue---and the uninstall reinstall. That worked perfectly. My panic attack is over. I strongly suspect something was rotten in Denmark with the update. Of course it could have also been a download error or an installation error, but there had been no indication of any of these. Anyway, my panic attack is over--if it ain't broke don't fix it.