I just updated Lightroom CC to the latest release. It works fine, but as soon as I quit the program, it won't start again. In the Task Manager I can see, that a process "lightroom.exe" remains after program closure. When I abort this process, I can start Lightroom again. I already tried to sign-off at Creative Cloud and sign-in again without success. My Operation System is Win8.1.
I have the same problem......
I created a new catalog and imported all photos from the old catalog and the error does not occur anymore! So it seems, that the catalog was erroneous => solved, no Software bug.