I have a nasty bug which I am having great difficulty fixing. I was able to play through the Vampire quests perfectly with a fairly recent character. I'm trying to use an older character to play through the Dawnguard side now, however am unable to complete the Chasing Echoes quest.
More specifically, the quest is started, but not added to my journal. The quest entries pop ups appear as normal when progressing, so it initially seems to work. However, I am unable to progress to the courtyard stage of the quest. I enter the courtyard, but am not followed by Serana (or any other followers, for that matter). Teleporting Serana into the courtyard with "moveto player" does not progress the quest, her scene doesn't trigger. The sundial pieces are also not present in the courtyard. The stage of the quest (DLC1VQ04) is 25, which as far as I can tell is what it's supposed to be.
Another possible symptom occurs when I tell Serana to wait after she starts following me for the quest. I am unable to tell her to resume following me.
I don't think it's related, but my character has completed the main quest of Skyrim, but has not sold the elder scroll to the College.
Attempting to disable some of my mods does not fix the issue, even when backtracking to before the Prophet quest, or before even joining Dawnguard.
Here is a list of running mods, in the order loaded:
Dawngaurd.esp
ClimatesOfTamriel.esm
HighResTexturePack01.esp
HighResTexturePack01.esp
Chesko_LoreBasedLoadingScreens.esp
ClimatesOfTamriel-Dungeons&Interiors.esp
PlayerHomeMapMarkers.esp
BDO.esp
Better Followers - SBP.esp
Better NPC - Faction Pack.esp

My other character was using these same mods, and Dawnguard works fine with them.
With my current character, I attempted to disable the BDO, Better Followers, and Better NPC mods.
Unfortunately due to computer issues, I do not have the list of all the mods that were used with this character over my entire play time. Everything else seems to work, however.

Any help would be appreciated.

PS. Wish we had the sources to the scripts right now, then I would be in a better position to fix this myself. *hint hint Bethesda *

UPDATE*: I started a new character with one additional SKSE mod. The "Skyrim -Community- Uncapper" Mod. I was still unable to progress to the courtyard.

Thanks

*New post because I am impatient egoist**
**Not really I've been working on this for days

UPDATE 2: Reinstalled Skyrim, loaded it with nothing but the official mods (including the texture pack), started a new game, and was able to get through the Chasing Echoes quest on the Dawngaurd side.

Same problem here.
Only mods which match yours are the High Res Texture packs, and those have empty esps.

I did notice that for some reason Stage 10 did not seem to fire.

Dexion's reading of the Elder Scroll has given rise to more questions than answers. The Moth Priest saw a vision of a weapon called Auriel's Bow, but Serana and I need to locate two more Elder Scrolls in order to unravel the rest of the prophecy.

It does this:

;This it init in DLC1VQElder - RPNC start FGAlias_DLC1VQ04RNPC.GetActorRef().EvaluatePackage()Game.GetPlayer().AddToFaction(pDLC1VQDoorBlockerFaction)Alias_DLC1VQ04RNPC.GetActorRef().AddToFaction(pDLC1VQDoorBlockerFaction);Enable the courtyard crestspDLC1VQ04CrestToggle.Enable();Make sure balcony door is lockedCastleController.LockBalconyDoor()DLC1VQ04RNPC.Start()SetObjectiveDisplayed(10,1)

This not firing would explain the problem we are both facing, though why it is not firing when the conclusion of Prophet sets this stage at 10, I have no idea.

After recompiling this script snippet, DLC1_QF_VQ04Hunter_0100284F, the quest now appears in the active quest log.
If memory serves me right, this was one of those odd loose files in the scripts folder just after downloading Dawnguard.

On a side note, this PEX file is not in the Dawnguard.bsa file so NEVER delete it from your scripts folder.

Edit: Confirmed in play, this is the fix.