LR 6 on second mac

Hello everyone,

New to the forum here and please bare with me on my technical English  

I've bought LR6 a few years ago on a cd version and installed it successfully on my 'mid 2011 iMac' (a few years ago)

Today I ran into a problem, I copied the cd on a usb drive and wanted to install the same LR6 on my '2018 MacBook Pro'.

Everything went well until the install wizard asked for the serial number, which I entered correctly.

When I entered the serial number the wizard said;

'Verification of legitimate adobe software has failed' (translated from dutch to English, so text may vary)

So how come that I can't install this LR6 on a second device?

Why does the program think that it isn't a legit serial number?

Thanks for reading and hopefully this problem gets solved.

Greetings,

didaL6