Hello Bullets, welcome to the forums!
Would you happen to have the steam version of the game?
If so, then you do not need to download and manually install any patch. Steam does it automatically. Since the installation path varies for a steam installment, the non-steam patch will not find the game. That's a possible cause for that error. You don't have to do anything else in that case, you should be on the right version already.
Note: Due to a fault at steam, your ingame version number might not update, making you think you're not on the right, latest version, but steam DOES actually update your game to the latest version despite of this confusing fact.
Regards,
Fred