Why doesn't the scripted sequence play?

Hi, I am trying to make a little singleplayer map for Half Life 2:Episode 2 but there have been some complications.
First of all, you start off in a room with a crowbar. There’s a door infront of you. You hear metropolices approaching.
They knock on the door, and then kicks it down.

That’s the story so far . Remember im just doing this map to practice.

But I can’t make the metropolice knock on the door.

Look at this video, and you’ll understand what I mean.

And here’s some pictures from Hammer Editor.


Showing of the scripted sequences (knock sequence is played first)

flags , knock sequence

another overview

Why doesn’t the first sequence (knocking) play properly?
Thanks in advance!

Do you have a trigger_once that tells the scripted_sequence(s) to start?
Alternatively if you want it to start when the map spawns you, use a logic_auto and tell it to start the scripted_sequences