Anithinks gives good advice
However I have noticed that your Load Order is pretty much a mess:
02 Oscuro's_Oblivion_Overhaul.esm [Version 1.33]
Either upgrade to http://tes.nexusmods.com/downloads/file.php?id=15256, (In Downloads scroll down to Updates and download the OOO 1.34 Beta 5 Patch, Install it after version 1.33 in BAIN) or you could wait until version 1.35 comes out of beta (hopefully by the end of this month :fingers crossed:)
07 Unofficial Oblivion Patch.esp [Version 3.2.0]
This needs updating to http://tes.nexusmods.com/downloads/file.php?id=5296. You must have missed this when you upgraded the other parts of the UOP since all of them are up to date (except for an issue I'll point out later). Go to the link provided and in Downloads, scroll down to the Updates section, and download the manual update and install it in BAIN after the main UOP file.
08 UOP Vampire Aging & Face Fix.esp [Version 1.0.0]
You can drop this esp. When rebuilding the bashed patch, click on Tweak Assorted and tick the box next to UOP Vampire Aging & Face fix (In fact if you are using the latest version of Wrye Bash (295.5) it could well be already ticked since it already preselects any necessary tags in your modlist)
09 Oblivion Citadel Door Fix.esp
Ditch this, it isn't needed at all.
0D Living Economy.esp
0E Living Economy - Items.esp
0F Cutthroat Merchants.esp
Consider upgrading to http://tes.nexusmods.com/downloads/file.php?id=25078, it can do all of the above and so much more in just one esp and is also completely bug free (Uninstall the above first and make a clean save, then you are perfectly safe in installing EE). Indeed all of The Nice One's mods are worth having, each one seems to be the best of that type of mod available. You already have Enhanced Hotkeys and
HUD Status Bars.
1C EVE_StockEquipmentReplacer.esp
41 EVE_StockEquipmentReplacer for OOO.esp
You should only be using one of these esps, not both. Use the one for OOO since that's what you have installed and ditch the other one.
1D MaleBodyReplacerV4.esp
Not critical but there is now a http://tes.nexusmods.com/downloads/file.php?id=40532 available for this mod.
34 DLCThievesDen - Unofficial Patch.esp [Version 1.0.10]
35 DLCThievesDen - Unofficial Patch - SSSB.esp [Version 1.0.5]
This could well be critical to your problem, you do not need the SSSB esp since the above one already contains the fix. Delete it. In fact this esp should no longer be in the archive but Kivian forgot to remove it when he released the update. He has since moved on elsewhere (6 letter word beggining with S, It'll come to me sometime...:X) and has yet to return to tidy things up.
3D OMOBS Optional Combat Settings.esp [Version 1.0]
Don't use this esp, this is already part of the OOO mod, it's only any use if you don't already have OOO installed.
4D Harvest [Flora].esp [Version 3.0.0]
4E Harvest [Flora] - Shivering Isles.esp [Version 3.0.0]
4F Harvest [Flora] - DLCVileLair.esp [Version 3.0.0]
50 Harvest [Flora] - DLCFrostcrag.esp [Version 3.0.0]
Upgrade to http://tes.nexusmods.com/downloads/file.php?id=2037, there is a CTD bug involving Harrada Roots in the above version, Version 1.35 of OOO will have the correct version bundled with it.
** MMM-Cobl.esp [Version 1.69]
You don't have Mart's Monster Mod installed, therefore you don't need this, get rid.
** Item interchange - Placement.esp [Version 0.76]
5C Item interchange - Placement for Frostcrag.esp [Version 0.76]
Two issues here, firstly upgrade to http://tes.nexusmods.com/downloads/file.php?id=17557. You are also missing Item interchange - Extraction.esp, if you don't have this the mod simply doesn't work properly.
I'm guessing you haven't built your bashed patch(Is it currently an empty 0kb file?) because the following seem to be active:
1B DLCSpellTomes - Unofficial Patch.esp [Version 1.0.1]
1D MaleBodyReplacerV4.esp
2F Armamentium female.esp
3C OMOBS_SI.esp [Version 2.0]
3F ArmamentariumLL4OOO.esp [Version 2.01]
40 ArmamentariumLLMagicOOO.esp [Version 1.35]
41 EVE_StockEquipmentReplacer for OOO.esp
4A EVE_KnightsoftheNine.esp
4B DLC_MOBS.esp [Version 2.0]
4E Harvest [Flora] - Shivering Isles.esp [Version 3.0.0]
4F Harvest [Flora] - DLCVileLair.esp [Version 3.0.0]
50 Harvest [Flora] - DLCFrostcrag.esp [Version 3.0.0]
55 Midas Betterholy.esp
5C Item interchange - Placement for Frostcrag.esp [Version 0.76]
61 EVE_KhajiitFix.esp
62 Cobl Races - Balanced.esp [Version 1.52]
In Wrye Bash all of these should appear with green or purple text, this is telling you these mods should not be activated. All of the above should be deactivated and merged/imported into the bashed patch. To build a bashed patch, right click on the bashed patch esp and select Rebuild Patch (use the CBash version since it's quicker and you get to merge/import more stuff. If you are using version 295.5 of Wrye Bash all of the donkey work in terms of ticking the required boxes should be done. Since this is likely your first attempt at doing this all of the options will also be bolded. Whenever anything new is added to the bashed patch the relevent area will be bolded. Select the Rebuild Patch button and wait for it to process. It should only take a few minutes. When you reload your game I would reccomend you wait 72 hours for the game to respawn everthing and properly apply all the changes in the Bashed Patch
If you do all this it will hopefully fix your problem. If it doesn't then you may have to deactivate the Thieves Den esp (as well as the UOP patch for it) and load a save from before you started the quest. Make a clean save (ie a fresh save that isn't overwriting another) and then reactivate the Theives Den esp and try the quest again. If you don't have a save from before you started the quest then it pretty much means restarting your game I'm afraid.
Hopefully you find all this helpful. Please don't throw a strop at the work that needs doing, I've spent the best part of 2 hours typing up this post.
Artorius.