CTD around Solitude when doing 'Hail Sithis!' quest

[RanneRo]

Recently I got CTD whenever get near Solitude for doing Dark Brotherhood quest - 'Hail Sithis!'. No fast travel, no console commands, no walking (or swim) by foots to anywhere near Solitude.

I tried to get it completed via 'setstage' command, quest completed, and now I was able to travel to Solitude again! Huraayy!

That sucks. I want to do the quest, not 'setstage', really. Here are the last lines in the last second the game crashes out.

[02/01/2013 - 04:54:27AM] Error: Cannot call GetStage() on a None object, aborting function call
stack:
[DarkBrotherhood (0001EA5C)].darkbrotherhood.OnUpdate() - "DarkBrotherhood.psc" Line 220
[02/01/2013 - 04:54:27AM] warning: Assigning None to a non-object variable named "::temp4"
stack:
[DarkBrotherhood (0001EA5C)].darkbrotherhood.OnUpdate() - "DarkBrotherhood.psc" Line 220
[02/01/2013 - 04:57:27AM] Error: Object reference has no 3D
stack:
[ (0001E68C)].Sound.Play() - "" Line ?
[ (0007E287)].fxDustDropRandomSCRIPT.OnLoad() - "" Line ?

Someone please figure it out, mod or script?

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Edit: Something's wrong with Command Maro, now I realized that whenever I'm going near him I get CTD, the rest of quest is fine.

[sora3]

Got any other mods that might be editing the quest or the area around Solitude inadvertently?

[Mana Yakushima]

Go to solitude on a different/new character?

[leddis3]

Possibly something the NPC has equipped is causing a CTD?

What I normally do to troubleshoot is turn off half my mods, see if there's still a problem, then the other half and reactivate them a bunch at a time if that solves the problem.

If not I disable the meshes, textures, script and interface folders by renaming them temporarily and see if that stops the crashing.

[Arethiel]

If you have a mod that may affect Commander Maro, you might want to disable it especially any that were made for a previous patch.

[Voltranis]

I would save outside solitude, then disable ALL mods. Save on a DIFFERENT slot after you relaunch with NO MODS, then reenter Solitude. If there is no CTD at that point, try enabling mods one-by-one until you find the issue. If you still manage a CTD on entering Solitude, try to verify integrity of game cache by going into Steam>Right-Click Skyrim>Properties>Local Files>Verify Integrity of Game Cache.