The problem is that when I enter Dayspring Canyon to start the Dawnguard quest, the scripts do not appear to fire properly. Agmaer won't talk to me in his usual 'I'm so nervous' speech, Durak won't give me a crossbow when I choose the 'what are you using?' conversation option, and when I enter the fort Isran and Tolan do not converse. Speaking to Isran gives me the usual conversation where he asks me to go to the cave, but after the conversation he and tolan don't talk and I never get the 'Awakening' quest. Setstage and other console commands haven't been able to get me past this.
I tried disabling all kinds of mods, but this just broke my save really badly and caused CTD's; in the few cases where i didn't CTD after removing a mod, the issue persisted. The SKSE option to clean onupdate scripts didn't touch the issue at all.
In desperation I followed some instructions for cleaning out scripts from a saved game - I COMPLETELY removed ALL scripts from the save following the instructions here : Nexus Mod ID 31675. This actually fixed the issue, and I was able to proceed on through the game. Everything SEEMS stable, but this was a VERY VERY VERY drastic step and I'm concerned that this may have messed up all kinds of other things in the game. I still have the un-cleaned save I can revert back to.
Are there any other options or is there any way to manually start the script that normally runs when I enter Dayspring?