Hi,
have just bought HOI3+DLCs ... have only one CD-key get (asume for the main game - none for the DLC pack ..... :/ )
and ... this Cd-key is shown on paradox forum on try to reg my game "Invalid" .........

Any enlighten answer for this ?
DISCLAIMER >
I know i can the game play without any thing like CD-key ...
BUT - i have it bought, with real money and so i think i can get an "real" game where i can register on the Paradox forum the Game (as it sould be ..)

I had a similar issue, I made a ticket and someone activated it manually for me, so I suggest you do the same (provided you haven't yet).