Some versions of Shift 2 have a limited number of activations (usually 5). If you have rebuilt your PC multiple times, you may have "used up" your activations. You must "Revoke" the license before uninstalling the game, or contact EA Support to reset the activation count for your key.
The countdown began…
Because Shift 2: Unleashed uses an older version of SecuROM DRM, modern Windows users often run into "Invalid Key" or "Connection Error" messages. Nfs Shift 2 Unleashed Activation Key