Did you start a new game everytime you changed your scripts?
This error is most often caused by trying to load an old savegame, but 80% of the scripts NEED "new game" to initialize themselves, and if that initialization is missing the result is often "undefined XYZ for nil-class".
Second possible cause is a wrong script configuration (missing notetags, wrong variables or switches, and so on.
If that does not help you, we need links to all scripts to check them.