First of all, that command takes the Base ID, so you need to substitute "xx" for the source mods LO position. Secondly, you should probably stop using that command to prevent trashing your game.
Thanks for the info but I don't know how to find the source mods LO position! I need your help here.
And thanks for the other advice from the others I will take your comments on board and will not save a game when using these placeatme commands. Plus, to the first commenter, that code didn't work either! I can't get any knights to spawn!