Have you installed Lightroom 5.6 using Creative Cloud desktop App?
If yes, Quit Lightroom 5 and navigate to
mac hd/library/application support/adobe/lightroom folder
Then trash Lightroom 5 install cookie file
Launch Lightroom and try activating.
many thanks for the reply. I have fixed the problem by uploading from the original disk. it seems when you download straight from Adobe things get complicated.
That is great..the problem is occurring when you are installing using creative cloud app.