I searched and didn't find any mention of this. It was touched on at HBO but no real discussion took place.
These are slight spoilers to the comic. They don't tell the outcome or anything, just describe a point in the plot.

Colonel Ackerson is captured by the Covenant and is being interrogated by Brutes. They say they are on their way to glass Earth, and they are going to kill him during the victory ceremony. He interupts them by telling them that if they destroy Earth they will never find the "Key of Osanalan". He then says this, which is the most interesting part, "I just know that without it [the key] - the Halo will fail... Like it failed last time." He then tells them that it is located in Cleveland.

So... The Halos were never activated before? Or is the "last time" referring to the almost firing of Delta Halo in Halo 2? The latter doesn't make much sense, Guilty Spark didn't say anything like that. So I'm saying that the Halos were NOT activated 100,000 years ago. That would explain why there's still Flood everywhere. This is very confusing.

honestly it just sounds like something he came up with to throw them off the trail and spare his life for a little longer. Its a delay tactic. Plain and Simple. Now actually calling the Key by a name... thats worth noting.

Yes, that is possible. Also the fact the there is a human civilian who knows what the key is is worth noting as well. I don't think the makers of the comic would've done something as confusing as that as a "distraction". They would've made it very obvious to us humans, and probably humorous.

This is also being discussed here at CI:

http://www.bungie.net/fanclub/118020/Fo ... D=12445642

(SPOILERS AHEAD)

Ackerson & the key of Osanalan, I thought that was pretty funny--like he was leading them to some ornament in a mall or something, I wonder what it is.

I also couldn't help but feel self-conscious (in a funny, ribbing way) when the brute is bellowing out to the tremendous crowd "Lead us to the the key! You will be rewarded!" The wording of "You will be rewarded" regarding a key to a forerunner structure sounded a little familiar . . .

I actually thought the writing, on a sentence-by-sentence, character-building level was pretty solid. I was impressed with it, low-key on MC as it was. And it was funny when the voice asks from out-of-frame "you got a gun?" We expect MC and then next page its . . . well, not. Lots of intelligent pacing throughout.

hmmm, but the colonel telling the Brutes that the key of w/e is in cleveland might mean a continuation of the story of Jersey Morelli & Co.