I upgraded to Windows 10. iCloud wouldn't work anymore (just ground away consuming resources without uploading any new photos to Photostream), and today my LR CC wouldn't open. I got the "unexpected error opening catalog" message. Oddly, it works fine if I got to "start" and right click the LR icon under "all apps" and select "run as administrator". Obviously, I'm an "administrator" on this upgraded Windows 10 machine already, so why I'd need to do this I don't know. But it's the only way I'm able to run LR and have it load the catalog.