I fast travelled to the Dawnguard castle with Serana and a conjured Vampire dead thrall, and as I arrived, the Vampire dead thrall turned to ash as they normally do, I entered the castle, and completed my quest. When I exited the castle door I noticed the ash pile was still there next to the stairs, and I continue to see the ash pile each time I visit Castle Dawnguard.

I now see ash piles all over Skyrim that were not there before this vampire dead thrall incident.

• I have reloaded a save prior to the incident and the ash pile is still there.
  
• I have cleaned up my cache, and restarted the system right after I noticed the ash pile.
  
• The game has began to load very slowly, sometimes I've waited almost 2 mins just for the load screen to finish.
  
• The game continues to lock up randomly, this happened before and after the ash pile. I have accepted the fact the locking up/freezing screen is part of the game now.
  
• I continue to conjure the dead vampires, and most of the time the ash pile cleans up, especially vampire attacks in the towns.
  
• I chose to play as a Dawnguard.
  
• I have completed most of the Dawnguard quests.

I never had an ash pile issue before Dawnguard, is it possable it's related to Dawnguard only??

I am playing on a 250 gig well ventillated Xbox 360
I am a level 54 battlemage, wearing all magic enhanced gear. I use the Dragon Bone sword with health enhancement.

Have You tried leaving the Cell and waiting 30 In game days before returning?.

Yes I forgot to mention I waited 40 ingame days, and nothing changed.
Thanks for reminding me to post that:)

Yeah i had them in whiterun, think it part of dawnguard.

The ash piles not cleaning up has been present since Fallout 3. Bethesda said they fixed it in one of the earlier Skyrim patches, but I never noticed a difference.

Does it matter that much it is just a ash pile. It isn't like it is going to destroy the game. All it does is ruin the look for some people which is a stretch.

Ruins the look and contributes to save file bloating, which causes lag and performance issues. So yeah, I'd say it matters.

I just accused Serana of making too much mess, where ever she goes she leaves little piles of ash and some just never seem to clean up, one day I will go back and see if I can tell where she has been. But I also had that problem before the DLC.

Thanks for your comment, but I'm not concerned about the look of the game, I'm concerned about how the ash piles are affecting my gameplay. As I mentioned in the OP my game has really slowed down to a crawl during loading. So yes it does matter that my game has suddenly changed due to a possable corrupted save.

Well in the interest of ash pile clean up, maybe we could all list where our offending ash piles are and that will give a clue perhaps as to which areas are at fault. Keeping in mind it does sometimes take a while for even the properly working ones to vanish.

I have uncleaned ones that have been there for ages in
Riften
Winterhold
Wolfskull Cave (lights and all were still going long after the quest was completed)

And Serana left one in Windhelm which is not looking like it is going to vanish.

When I get a chance I will have my first character check around a bit, there are other places I have noticed the offending piles of ash, when one of my characters has returned much later.

Bethesda hasn't been able to fix ash piles in about 5 years since FO3 came out.

Don't count on anything changing.

ash piles don't go away i have a ton of them all over morthal. from when I blasted my way out of jail and that was months ago.

I still have Arcano's ashes, & that was early in my game, right after the 1.5 patch. I think that was 700 in game days ago? Could be wrong about that but certainly over 2 or even 6 months in-game. That's the only one I know of, but then maybe because it's the only in-doors place I killed someone that I keep returning to. I haven't experimented with staying away from that site for 30 in game days.