Rockstar Activation Code Appear on start up of GTA 5...

[Nocturneve]

Hi, can anyone please help me how to actually fix it? i was trying to play GTA online on my PC, yet it said that i need to active my code, so i looked up on google watched some vids on how to solve this problem and i got the CD keys through my Steam Library and it says "Rockstar Activation Code Already in use."

another thing, when I click on steam about game issue on "I'm having trouble with my retail CD Key"it says:

"You already own a copy of this game on Steam. CD Keys cannot be used to gain extra copies of the games or Steam Gifts.
If You are attempting to register a key for in-game and having trouble, please double check the instructions you received with the key to make sure it is redeemable on Steam. Often in-game items are redeemable within the game itself. If you continue to have issues please contact the original seller of the key for assistance. For more information on retail CD keys, please read this FAQ."

Can someone actually help me how to fix it???