Classic, you can read about it here (choose one):
[url]Problem with Enemys Firing]
[url]multiple spawned bots but only one shoots]
[url]Turret fire]
So it doesn’t crash when you switch to the animation with no collision mask, but crashes when you switch back to the default animation?, not sure, try to add a collision mask to the invincible animation and let me know if still crash.
Also, what is the error in the console? (in Firefox, you can open the console with Ctrl+Shift+I or Ctrl+Shift+K) 