When approaching Caldera on the way to Caldera Mine (from any direction, but have been going on the roads) for the quest, the game locks up then CtD's. Can save right beforehand, but after loading the save and attempting to continue walking ahead, crash happens again.
Mods loaded, in load order
Oblivion.esmMorrowind_ob.esm
Unofficial Oblivion Patch.esp
Oblivion Citadel Door Fix.esp
UOP Vampire Aging & Face Fix.esp
DLCShiveringIsles.esp
Unofficial Shivering Isles Patch.esp
DLCBattlehornCastle.esp
DLCBattlehornCastle - Unofficial Patch.esp
DLCThievesDen.esp
DLCThievesDen - Unofficial Patch.esp
DLCThievesDen - Unofficial Patch - SSSB.esp
DLCMehrunesRazor.esp
DLCMehrunesRazor - Unofficial Patch.esp
DLCVileLair.esp
DLCVileLair - Unofficial Patch.esp
DLCHorseArmor.esp
DLCHorseARmor - Unofficial Patch.esp
DLCOrrery.esp
DLCOrrery - Unofficial Patch.esp
DLCSpellTomes.esp
DLCSpellTomes - Unofficial Patch.esp
DLCFrostcrag.esp
DLCFrostcrag - Unofficial Patch.esp
Knights.esp
Knights - Unofficial Patch.esp
Morrowind_ob - UCWUS.esp
Morrowind_ob - MorroblivionTreeReplacer.esp
Morrowind_ob - Conversation.esp
Morrowind_ob - Chargen and Transport Mod.esp
Morrowind_ob.esp
Cary all you want-5118.esp
MiniMap.esp
Morroblivion spellmaking and enchanting stations.esp
Morrowind_ob - Morroblivion Maps.esp
MaleBodyReplacerV5.esp
Vampires - No Sun Damage.esp
One of a Kind Weapons.esp
OoaKW - Staff of Worms.esp
MorroblivionNewMap.esp
Mods have been sorted and ordered by LOOT. No sure if the vampire mod affects Morroblivion's Vvardenfel Vampirism, but don't believe it to be responsible as the CtD occurs without it as well.
I've been trying to track
I've been trying to track down variations on this CTD -- basically a crash as you are moving towards specific area, usually when a new cell has loaded or trying to load. Open your "\Documents\My Games\Oblivion\Oblivion.ini" file and try to find this code block:
If those two lines are set to 1, try setting them to 0. Let me know if that helps.