I have tried all the suggested remedies, from deleting the opm.db file, to reinstalling the latest version of the Creative Cloud Desktop application. If I sign in on Adobe.com, I can sign in and look at my registered Lightroom just fine with the correct Serial Number on record, but I cannot sign in from my LR6 to upgrade it. When I click the Sign In tab under Help, I can enter my login and password, but instead of logging in, it comes back with the message "You have been signed out" every time.
OS: Windows 7 Ultimate 64-bit
LR: Version 6.0 Camera Raw 9.0
Thank you for that link. It worked like a charm, 188 MB download, followed by unzipping, installation and a reboot. LR6.1.1. working.
But I still cannot Sign In! I hate this Creative Cloud Crap.