Hey, I assume you're referring to Knytt Stories Plus? In this case, you need to make sure your level is set to Format 4 - in your script, look for the following at the top:
[World]
Name=
Author=
Description=
Category A=
Category B=
Difficulty A=
Difficulty B=
Difficulty C=
Size=
Format=4 - Set this to '4'!
That tells the editor that it's dealing with a KS+ level, and so it activates the extra features, as well as blocking it from running on vanilla KS.
You should also make sure you've downloaded the most recent version of the KS+ editor from egomassive's website and are using that instead of the default editor, though it sounds like you're already doing that.