A "Wave Motion Cannon" is activated and sets on the field for turns. Now the owner decides to activate its effect, sending it to the graveyard. It would be put onto the chain as Chain Link 1. NOW, simply, why can the opponent not chain "Barrel Behind the Door" as the ruling states?
"¢ You cannot activate "Barrel Behind the Door" against a Continuous Spell or Trap Card, an Equip Spell Card, or a Field Spell Card. So you cannot activate it against "Magical Thorn", "Dark Snake Syndrome", "Wave-Motion Cannon", or "Black Pendant".
"¢ You cannot activate "Barrel Behind the Door" against a Continuous Spell or Trap Card, an Equip Spell Card, or a Field Spell Card. So you cannot activate it against "Magical Thorn", "Dark Snake Syndrome", "Wave-Motion Cannon", or "Black Pendant".