Okay, so I was trying to help the Followers of the Apocalypse create a deal to get medical supplies from anywhere they could, when I took a break, I came back and tried to load my game, it told me that the DLC was no longer available. I was playing for about 2 hours before this, but all saves worked fine up until a certain part in that quest, which sadly, I cannot pinpoint as I didn't save during the quest. I had gotten up to the point where the Atomic Wrangler agreed to supply, I had just informed the doctor (I forget her name) that they had agreed.

I do not own any of the pre-order packages.

My save file is 40 hours and I have had no problems (except a couple of crashes) until this point.

I loaded a previous save file, it worked as normal.

EDIT: After playing through the "quest" again, doing everything exactly as I did when the bug first occurred, I am unable to replicate the problem, which, at a guess, means that the bug will only manifest under extremely specific conditions.

Im glad you were able to recover your game but mine is still failing at loading with the corrupt save message At least now I know this doesnt happen to only the preorder dlc people

I went into vault 34 and then it all started going downhill. I keep getting the dlc missing message. This is impossible. I keep saving every 10 mins but every second save becomes corrupt and now they all are. This is so frustrating. Thanks Obsidian. Never experienced any game breaking bugs in fallout 3 or any other game for that matter and that makes Bethesda more competent then Obsidian and there dodgy technical staff. Does Obsidian have bad managers that cut corners to get it out on release date or something? Lets hope they fix this in there first patch and sorry to slag off but I am annoyed deeply.