The first point is that you should never ever completely trust an answer that is posted here. It's very easy to forget some minor detail of syntax when you are answering a question. When you get an answer to your question you must spend some time looking at the command ref, searching the FAQ and forums for futher and advice and playing with the commands. You should not even attempt to put the answer into your mission until you fully understand the commands it uses. (Of course you can use your mission as an example mission to help you understand.)
The next thing to do if something doesn't work is to simplify it. Never mind 6 scuds, make it work with 1 scud first.
"mission (" error is easy to solve, you just need to find the mission bracket.
Unknown operator can mean anything .. it basically means the game can't make sense of the command.
Hints are very useful for debugging, you can use them to let you know what is going on.
So here's what you do. Create new mission. Insert a player unit and one scud, named scud1. Create a trigger
Condition: alive scud1
On Activation: hint "alive"
Test it to see if it works.
Now add another trigger
Condition: not (alive scud1)
On activation: hint "dead"
Give the player unit a LAW and try it out. When it works, add numbers to the countdown fields. When that works, change the trigger type to end#1. When that words add another scud and so on.
If it doesn't work and you really can't figure out why, make post in your existing thread saying exactly what you did and exactly what went wrong.