Certain Entities are unscriptable?

[Mudbill]

Certain entities cannot be modified like this unfortunately. If you open them in the Model Editor, you can check their type under Settings > User Defined Variables. If this is set to StaticProp, it will be limited. You can fix it by changing it to Object (Static) instead, but you must save it as a custom entity and use that instead.

If you just want to make it disappear, you can try SetPropActiveAndFade. I think it works on StaticProp type entities, unless I'm misremembering.