Seems that catalog is corrupted beyond any repair.
You should have multiple backups of the catalog that have been compressed into ZIP files. Normally they are made once a week and the default stored location is in a Backup folder under the same folder your catalog is stored in. They are in dated folders under the backup folder. So find the most current date folder, open that and Unzip the backup catalog. Then you can copy it over the top of the corrupted catalog and then LR should open. Or copy it to some other folder you create and hold down the Ctrl key (that's on Windows so it might be the Command key on a Mac) and you will get a dialog windows asking which catalog to open. At the bottom is a button that says "Choose a Different Catalog..." click that and browse to the folder you copied the unzipped backup catalog to.
Thanks for the quick response. I tried to open the back up, no error message, but it timed out and I had to force quit. I tried to copy the backup catalog over into the main folder and got the same original error message. What next?
Make a new folder anywhere on your drive, something like LR Cat V2. Then Copy that backup catalog to that new folder then double click on it.
If you get the same error and or LR crashes then you more than likely have some type of hardware problem that has corrupted the LR install.
You can try uninstalling LR then use the CC cleaner app to wipe out all traces of LR then reinstall. Your catalog and any backups of the catalog won't be affected by doing this.