The only way the old file would be the cause is if you had started the game prior to adding the script and saved it. Even if you loaded it after adding the script and saved again, the damage has already been done. Many scripts set up things with actors when you start a new game, and that is all saved in the save file. If you don't have a script and just let the actor setup happen normally, then you add a script that WOULD have set up some custom actor stuff, and go back to your earlier save file, the actors there still don't have those things set up (because they're saved with the save file and are not recreated every time you load the game).
This is a very common issue with adding scripts and loading old save files because you don't want to start playing over again. If you add a new script, play a saved game that was made prior to adding the script, and you have problems, your first action should ALWAYS be to start a new game and see if the problem still happens. Many times, it won't.
This thread is being closed, due to being solved. If for some reason you would like this thread re-opened, please report this post and leave a message why. Thank you.