If you have an old, unused "Multiplayer ID Key" from 2006, the official Ubisoft servers that once validated it are offline forever. You do not need the original key anymore—you need a workaround .
Even if you have a valid key, you might encounter errors when typing it into the multiplayer prompt. Several technical shifts cause this issue on modern versions of Windows: 1. Server Deprecation and Master Server Shutdowns Ghost Recon Advanced Warfighter Multiplayer Id Key