If the registry fix does not work, consider these common causes and solutions found across community forums:
Are you currently using the or an older physical copy of the game? sniper ghost warrior serial key is invalid
This is a known fix for the GOG version . The game looks for a specific registry entry that might be missing if you moved files or had an interrupted install. Press Win + R , type regedit , and hit Enter. If the registry fix does not work, consider
Sniper Ghost Warrior - "Serial key is invalid", page 1 - GOG.com page 1 - GOG.com