Green Goblin: Does a stun status prevent Norman Osborn from using his forced interrupt?

Yes, a stun status card will prevent Norman Osborn’s activation. This is due to the rule under “Status Cards” on page 16 of version 1.1 of the Rules Reference (That rule states: “Status card abilities have timing priority over all conflicting card abilities.”

So, the game will tell Norman Osborn to attack (either because of a game step, such as step 2 of the villain phase, or because of a card ability, such as the Assault treachery). Because status cards take priority over all other abilities, the game will check if Norman is stunned. If he is, the stun status card prevents the activation; if he is not, Norman’s “Forced Interrupt” ability kicks in.