Scripted Npcs won't trigger

I'm having a problem with npcs that are scripted to find the player character (like the courier), they simply do not do what they are supposed to. I'm aware of the courier fix with prid and moveto player, but this seems to be affecting all the characters that act in the same manner. Does anyone have any experience or tips when it comes to this, or at least how i can find out what the problem is?