Just yesterday I played a game where I stupidly ended up on top of an asteroid with my E-Wing. I fortunately took no damage, however my ship was perched in such a way that the right edge was off the asteroid, however right infront was a tiny piece of asteroid.

My opponent stated that I would have to roll for the asteroid hit as I was coming off it since the template would (and it most definitely would) have overlapped the asteroid.

Wanting to avoid this I posed the idea of using my advanced sensors to barrel roll off the asteroid since my ships right side was off of the asteroid.

His opinion was that I couldn't do that because I was on an asteroid and thus could not take my action at that point.

I contested that it would be unfair of that to occur since I only loose my action if I end up on the asteroid at the end of my turn or the manoeuvre template overlapped with an asteroid.

Keeping within the 'fly casual' spirit, we both concluded to let me barrel roll off the asteroid since it was an intelligent and tactical way to avoid the otherwise inevitable damage roll.

I would, however, like clarification as to the rules of using Advanced Sensors while you are on an asteroid.

You ARE allowed to barrel-roll off of an Asteroid with Adv Sens, assuming that the barrel-roll template does not hit the asteroid.
Your opponent was simply wrong

When you start your turn on an asteroid you can use Adv. Sensors to barrel roll/boost off of it, as long as the template used does not overlap any part of the asteroid.

Then complete your movement as per normal activation.

Boosting and Barrel Rolling cannot be done if their is an overlap occuring. (You get to go back and select a different action or another direction of laying the template).

The key part is that being on an asteroid doesn't prevent you from taking actions, it causes you to skip your perform action step. Advanced sensors gives you the chance to perform an action at a different time, and also causes you to skip your perform action step. Since the action is being taken outside of the perform action step, the asteroid has no effect on it (other than the regular restrictions on boost/rolls). Now, if advanced sensors said something like "your perform action step occurs immediately before you reveal your maneuver dial" then the asteroid would cause problems, but it doesn't say that.

Now, if advanced sensors said something like "your perform action step occurs immediately before you reveal your maneuver dial" then the asteroid would cause problems, but it doesn't say that.

I actually think this would still work, assuming it was still phrased to be optional. Even if it was actually moving your perform actions step to before revealing the dial, at that point your final position or maneuver template that round has not overlapped an asteroid so you wouldn't be skipping your perform actions step. Purely academic point, of course, doesn't change the answer to this question at all.

Even if it did, it would not matter. Being perched atop an asteroid does exactly nothing except prevent you from making attacks. Overlapping the asteroid with the ship or template when you execute a maneuver is what triggers the damage roll and skipped action step. Advanced Sensors effectively lets you take your action before it would be lost to a collision, so using it to barrel roll off an asteroid is legal and effective. You could also boost off an asteroid but doing so just to get off the rock would be a wasted action. For the boost to be legal, the front of your ship would have to be clear. If that is the case, you can execute a normal maneuver without ill effect. Remember that only the template and final ship position matter. Starting a maneuver on an asteroid only hurts you if part of it overlaps your front guide section, forcing the movement template to overlap the obstacle.

In the rule book on page 20 it explains how to deal with this. Forgotten Lore gave the rule pretty well word for word. It isn't like stress, you can perform actions, but you must "skip the perform action step". That means that anything from Adv Sensors to Lando, to Squad Leader can get you off of that Asteroid. If you can get that barrel roll before the shooting phase, you get to attack like normal as well.