Ok, so after getting this error about 2 days ago (and being enormously frustrated) during my 15th hour of play, I was lost at what to do. My last nearest save was @ 8 hours and I had a lot of different things I did.
I decided to jump back in there, retrace my steps and figure out if I can retrigger this error but in a more controlled manner. So starting at the 8th hour I replayed all the stuff, up to and including Vault 3 (which I am guessing is where my error stemmed from) while also actually getting a lot more gear, caps and levels. Just on the side, my first time around I had ~ 700 caps after buying stuff, the 2nd time around (post anolysis of error) I am at 3900 caps....so I am actually better off rofl. Anyways, as I played I had 3 save files at all times, I would swap between Auto save/manual save and then have the third save open for whenever I entered areas.
As I got to Vault 3, the "source" for a lot of errors, I saved manually in slot 3, and kept slots 2/auto for vault three and only vault 3. I played all the way through, killed everyone I could and got to moto runner and killed him. Now I don't recall where I read this but I had seen someone write that the "REVERSE PULSE CLEANER" http://fallout.wikia.com/wiki/Reverse_Pulse_Cleaner could be a potential threat. So I saved my game (Slot 2) before I grabbed the pulse cleaner, grabbed the cleaner, saved my game AGAIIN (in a new slot) then had an auto save (So I had 3 saves, 2 after pulse, one before). I kept running around and doing things, I tried to swim under water and ended up drowning. No biggie right? I''ll reload...not! Lo and behold DLC error. I tried to load the save (2) BEFORE the pulse cleaner pick up, ALSO DLC ERROR. I tried to load the save BEFORE vault 3 (3) BINGO! I replayed the whole vault 3, did NOT grab the pulse cleaner and have had no problems so far (continued forward to Camp McCrarren) and am running strong.
So, in summary, the pulse cleaner, which is needed for the quest http://fallout.wikia.com/wiki/Still_in_the_Dark could be the cause of this bug. I am assuming if you are not on the quest (which I wasn't at the time) it will crash game saves etc. I might go back after I do a bunch of stuff and see what happens and perhaps repost, but so far this is the one point I have anolyzed that can cause the DLC error. Happy Hunting!
sorry but i think your theory is wrong because the stupid DLC error has happened to me 4 different times on four separate locations on separate random times. it usually triggered after i reloaded an auto save shortly after saving.
Here are the locations that happened to me
1. Gun runners at the kiosk
2. big tops casino in the lobby
3. Michaelangelo's in the repair room
4. Black mountain in the jail room
i have lost over 175 hours of game play it is so frustrating. Ive decided not to play again until they patch it.
in conclusion i dont believe it is triggered by a certain quest or location though i could be wrong im just trying to help Bethesda.