Hmm, hast du das schon versucht? (aus dem offiziellen Forum)
Ist zwar nicht exakt der gleiche Fehler, aber das Vorgehen wird bei den meisten Aktivierungs-Problemen empfohlen.
Error: You are receiving the Error ‘Product Key already Active’ message
Fix: You need to delete the certificates and re-activate the game
1) On receiving the error, please uninstall the game
2) Please navigate to the following directory:
XP users: C:\Documents and Settings\All Users\Application Data\Sports Interactive\Football Manager 2009 Certificate
Vista users: C:\Program Data\Sports Interactive\Football Manager 2009 Certificate
3) Please ensure that it is the \certificate directory you are located in
4) Delete all content
5) Reboot the machine
6) Re-run the installation program and retry activation - ensuring you have 'verified' your key using the following website:
http://keylookup.fm2009.softanchorinsight.com/7) You should now be activated