If it's not firing, you can force it to start via the console and then talk to Lan directly. It's been like 5 years so I can't remember this off the top of my head and I deleted all the modding stuff off my computer ages ago, but you can get the next stage to talk to him one of two ways:
1. Open up the console and type sqv <Quest ID> with the ID being the intro quest. It'll be something like Myt_KarnaQuest_Intro, you can find it with help myt or mythos command in the console.
Because I work in increments of 5 or ten in most cases, if the stage is currently at 5 to start the dialogue scene with Lann, enter setstage Myt_KarnaQuest_Intro 10 for example and then activate him to talk.
2. If you're familiar with xEdit, you can skip messing with the console and find out what's the next step by checking the Quest tab, then setstage as before.