I made a few erroneous assumptions in the post above. When you setSimpleTaskDescription on an existing marker it will automatically transform into a yellow circle. That's the only reason to use one of the invisible 'Empty' markers to the define the destination for your objectives in the editor. Game wise, a marker is a marker is a marker. OK? It just looks better if your new yellow marker isn't spawned on top of an already existant marker, in another colour. Enough of that for now. Lets take a look at a working sample code and explain what it actually does. These are a quotes from the briefing script in one of my missions:
tskObj1 = player createSimpleTask ["Insert on Utes."];
That's the first step when you are creating a task. As you can see this is an instruction that tells the player to 'insert' on Utes. It's purely Eye Candy. As you've already figured out it serves little purpose apart from adding to the players immersion. We still cannot check if the created task has been accomplished ingame or not. We simply cannot use the created simpleTask just yet. Let's continue with some more Eyecandy (it will become important later on though). Lets add a description to our simpleTask:
tskObj1 setSimpleTaskDescription ["Board the helicopter and order insertion (0-0-1)", "Insert on Utes.", "INSERTION"];
The above quote denotes (in order of appearance) the text the player will see in the right hand-box, next to the task head line (when he/she highlights the original task headline with a single mouse click), and the listbox headline above. The quote serves no other purpose but does indeed look good on screen. In order to make the entry useful in the future you must use the exact same phrase when you define the second quote here, as you did when you defined the first quote above (in this case "Insert on Utes"). Now it's time to decide wich task should be active on mission start. Since my example only includes one task, I'll set that one to active using the following code:
player setCurrentTask tskObj1;
Since you wanted to add a clickable hint to the briefing (player double clicks on "Insert on Utes" and map centers at the object destination) we must add another line to our briefing script. It goes as follows:
tskObj1 setSimpleTaskDestination (getMarkerPos "destinationObj1");
destinationObj1 is an empty marker I've already placed on the map and named myself. As mentioned before you may use any type of marker and make up any name to your liking. The effect is as follows: When the player double clicks the task in his/her briefing, the map will center on the marker. Exactly what you wanted, right? Three things are important here:
1) You must use createSimpleTask before you setSimpleTaskDescription
2) You must setSimpleTaskDescription before you setCurrentTask
3) You cannot setSimpleTaskDestination unless setCurrentTask has been executed in the script.
Read the three steps again, because the chronology is important here. That's where you screwed up in your quoted example. You used setSimpleTaskDestination before setCurrentTask. Otherwise your code isperfectly fine.
SIDE NOTE: I've been fooling around with this game for 9 (nine) years, and your question almost forced me to my knees, trying to help you. You've managed to solve most of the problem at hand singlehandedly, and I'm sure you'll manage to solve almost any problem you'll encounter concerning ArmA2 scritpting. Good job! I'm impressed.