Hecklar

Warzones, is the issue. Uninstall it for the duration of that part of the storyline.

Luke, uninstall the mod Warzones from your NMM for the duration of that part of the quest, it seems to be the culprit of this problem.

Confirmed, Warzones appears to be the problem.

I'm having the same sort of problem.. At that time in that area... But I'm on the storm-cloak side preforming the siege, if I get anywhere near the gates, it Ctd's me.