Voici en anglais la réponse. La solution consiste à supprimer le message en décochant toutes les cases relatives à ce logiciel après être entré dans executer puis msconfig puis startup. Cette dll n'est plus nécessaire !
The file THX2CF64.DLL is related to software "Sound Blaster Cinema".
After a recent update of this software, this file THX2CF64.DLL is no longer in included or used.
If you after an update of this software get an error message like "Can't find THX2Cf64.dll" at Windows startup, the cause is most likely that the start up entry for this file has been accidentally left behind, allthough no longer necessary.
If you do not experience any problems related to your sound even with this error message, you can safely remove this left behind start up entry.
How to remove the Startup entry: Win XP, VISTA, 7: Press "Windows"-key + "R" to bring up the "Run" dialogue. In "Run" dialogue type "msconfig" and hit Enter Under the tab "Startup", uncheck any boxes relating to these files.