I was really looking forward to this.
Here's what I've done, and none of it works. I am a PC user.
I don't know of anything else to try.
This has worked for me, too. I hadn't switched mounts, so I guess I never had that, but I did have to wear the normal pajamas and it worked for me.
I never got to start the quest via the war table, but I was finally able to do so via the World Map. Everything was fine until the first Eluvian, and then, you guessed it, CTD.
I turned off the multi-sample anti-aliasing thingy/setting and so far no more CTD's. I have synced the nug. I can talk to everybody. I have gone through multiple eluvians. I even redid a couple of mods, though I don't actually see them. Give it a try if you are still having troubles. I figure if I have problems lated I'll try turning off the other anti-aliasing.
I can't even get out of the first area. My game first CTD'd during the cutscene before you're sent into the gardens after talking to the priestess type lady. Like, the first conversation of the expansion. When I reloaded I was just in the garden area where you can talk to everyone. Talked to Varric, moved a bit, crash. Came back in, talked to Blackwall and moved around a bit more, crash. Came back in, crash. I can't really do anything. My PC is nothing to sneeze at, I have a hard time believing it's me: http://pcpartpicker.com/b/snBPxr
Oh I also reset everything down, turned off AA, everything. Went to turn my settings down to minimal before it dawned on me. This isn't my problem. I have one of the best video cards on the market that runs every other game effortlessly. Tons of other people are having the same types of problems here. I shouldn't have to drop this game down to looking like the original Mario Bros just to play it.
I will happily submit any reports DA:I people want me to do, just fix your product. Please. I want to know how the story ends.
I know I tried several things before it worked for me. Have you tried everything listed? Sometimes it seems like the smallest change can get past the bad. Possibly adjusting your inventory and creating a new save will work. You did try without mods, right? That is, if you're on PC. A lot of them will definitely interfere with Trespasser. Do the Trials and Golden Nug work for you?
I'm sorry you're still having problems. I wasn't kidding about something small making the difference, either. Just like when somebody switched their mounts and then they were able to get started.
For example, in one of my previous games I went the Templar route but couldn't get to the final battle with the Envy demon, at least not so my people would work properly instead of looking and acting like stick figures. I don't like the active quest notice always being on screen, so I habitually turn it off (I really wish there were some way it just showed active in your menu without hogging space on your screen or minimap). However, every time I tried to engage - you guessed it, stick figures or even CTD. What finally worked was when I left it active and then I was able to move forward and take down that sucker with everybody moving properly.
I know it seems silly, but I can't help thinking that sometimes a little 'virtual grit' gets stuck in the game's 'gears' and needs to be shaken loose. If you've tried everything else people have mentioned in this thread, then try little offbeat things like that. And don't be afraid to change your HUD settings or other settings - you should be able to change them back with no problem. Good luck.