Nice descriptive title for a change, mainly 'cause I've spent ages hunting around for a solution myself, so if you're coming here for just this very reason, I understand your pain.

We had issues with mochibot on Invaders Must Die, but by then I'd passed it over to Mousebreaker so they had to deal with it in-house. It's the first time I've hit it face on so to speak.

To set the scene and get you in the mood, I've just finished the viral version of cronusX and wanted to try the version control that mochi offer, as that was one of the best things about gameJacket, plus I've added a twitter option to the game which I know is going to bite me on the arse with people bitching it's spyware etc. etc. so I wanted the option to rip that out if it was becoming too much of a ball ache.
I've also included mochi-bot tracking so Candystand can see how it's doing out in the wild, so I've dropped that in too.

Everything worked first time ( That's where it differs from gameJacket and it's constant security check failures ), gave it a quick test, all good. Ah, not all good, the transition craps out to a black screen.

Testing it locally ( Turns out I've not installed the browsers debug version of FP10 on the pc, how good am I ? ) it spat out an error,

Error # 2121: Sandbox Security Violation: BitmapData.draw

etc.

Joy.

Lots of googling ( To no real avail, hence this post ), seeing the only advice on the mochi forums that I could find was someone copying out some text from the Flash help ( Cheers for that, solves everything ) it turns out that the mochi-bot can't be on your root display object, as you get all the security violations when trying to use draw(); that you would if you tried loading in say an image and using draw(); on that ( It's a cross domain thing. To be honest life is too short to go into it, I could just copy from the as3 docs, but... ).

Basically, long story cut shorter, if you do something like:

MochiBot.track(this,"yourMagicNumber");

In your preloader ( Assuming that "this" is your main preloader class than extends MovieClip ) then you can't use draw(); in your main code.

To get around this, give it a movieclip instead, eg.

mochiBotHolder=new MovieClip();
stage.addChild(mochiBotHolder);
mochiBotHolder.addEventListener(Event.ADDED_TO_STAGE,triggerMochiBotTracking);

private function triggerMochiBotTracking(e:Event):void{
    mochiBotHolder.removeEventListener(Event.ADDED_TO_STAGE,triggerMochiBotTracking);
    Security.allowDomain("http://core.mochibot.com/my/core.swf");
    MochiBot.track(mochiBotHolder,"yourMagicNumber");
}

Now I'm not sure if you need the allowDomain(), but it works with it, and that's good enough for me after losing a good hour and a half to this little gem of a problem.
Because the mochibot code needs to hit loaderInfo.loaderURL via the clip you pass it, you have to add your holder mc to the stage, and then wait until it's actually there before calling MochiBot.track, otherwise you're in the land of null properties.

Now I'm not sure if you can kill that holder mc of after calling the track() method, it's like the allowDomain(), it works as it is, and I'm happy with that.

This has proved to be a fairly techy / geeky post, quite rare from me.

Squize.