Well, i never played Halo but i did play Freespace.
From the game, we know they are using the same shield technology on the Lucifer that is on their smaller ships. We know known weapons are effective against these shields on smaller vessels. This means known weapons in the game will have some effect on the Lucifer's shields as well, because it is the same technology. We know conventional capital ships are not using shields because of the power requirements to do so. We know the Lucifer has a number of super reactors to power its shields in order to overcome this problem.
Given these facts, it may be reasonable to conclude that the Lucifer's shields are invincible to all known weapons under normal circumstances, but if you throw in a multiplier of those weapons, bring enough of them to bear, sooner or later somethings gotta give, after all, you cannot beat physics!
