I have purchased every copy of Lightroom from 1 through 5, always on CD. And it's always updated perfectly, just type in the activation code from the last CD case and off I go.
This time I could find no-one who could sell me the update to Lightroom 6 on a CD.
So I downloaded it. And can't get it to activate. Every stupid code I enter from Lightroom 1.0 through LR 5 gets me the same answer, that the number is no good.
A working system goes broken.
I dread the day that LR goes cloud only.
Lightroom 6 is also available as a standalone version, you can buy it directly from Adobe.
Also, if you try and activate Lightroom 6 using the serial number between 1 to 5 version, it will not work.