I played assassins creed:black flag on my friends ps3 on his user but then he said I could create a new user for me to use. I copied the save data from his user to mine and then accidently deleted it from his user but when I go on the game on my user it won't let me open the saved data. Is there anything I can do or will I have to restart the game again?
Well, officially you're not supposed to be able to copy save data between users from what I've read from Sony, but apparently it is possible on some games.
You can find a list here that is kept current (at the time of this answer) that lists games that allow copying between profiles as well as other details.