Did you previously run a lightroom creative cloud trial? When your trial Lightroom CC subscription ends, you continue to have access to the Library, Slideshow, Web, Book and Print Modules, but the Develop and Map modules will be disabled, indicating the end of the membership. You can either subscribe to Lightroom CC or purchase Lightroom 6.
If you used a creative cloud trial and then bought Lightroom6 without creative cloud, see this link to serialize it:
If you did not use a trial or Creative Cloud at all, please let us know.
I have never used CC bought lightroom stand alone, have emailed you guys at least twice to stop forcing me to sign in and to quit telling me my trial had run out, not you have stopped me using the develop mode, SORT THIS OUT ADOBE, since when did you think you can force your customers to have to email you to use a bought product.
A very pissed off customer