So... I've noticed there are a lot of issues related to this quest. For me personally I had to try to catch the spy four times before he would actually come through around 1 am. Finally I do the turn that part in get sent to the monorail, and then everytime I run to the darn thing it just starts. I finally figure out that you have to run VERY close to it to get it to not start right away. So I eventually get onboard and I diffuse the bomb and get off the train, it starts and explodes anyways. My science and explosives skills are both over 60 so that isn't a problem, as well as having the deactivation codes. Trying to diffuse the bomb in any way results in a successful message, but the thing still explodes. I'm trying to go uber NCR so I can't just accept the train exploding and failure to save it. Is there a timeline anywhere to know when severe bugs like this get fixed? My understanding is that there are many, many people who can't successfully complete this leg of the quest.
For me I've already logged 25 hours playtime and I really don't want to start over when I feel like I've put this much effort into it. What else have you all experienced? Found a way to make it work? Please let me know!

Seriously guys, I really want to play but I can't until this quest is fixed!! Help?!

+1

So, understanding that the start of the quest doesn't bug if you hug the railing as you move I did the same thing leaving, and my quest continued to show success for stopping the bomb! Yay Right!
Well I go to turn it in and Hsu asks "What Happened" but I get no dialogue to report to him that the bomb is done. In order to complete the quest I guess you have to "fail".
Bummer.

meh, I just finished it with the train exploding. not big deal.

I read a few pages back that you have to listen to the conversation the spy has on the radio and then confront him.
Don't talk to him too early or it breaks this quest.

I have not got my 2nd character to this area to try it yet so I cannot be sure it works.

It seems, from what I've read and experienced, that the bug is a result from talking to Captain Curtis twice. This worked for me--here's what you should do to fix any bugs you're having with the quest:



Thanks goes out to Mr./Mrs. "Common" from Techarena forums, whom that quote should be attributed to. [http://forums.techarena.in/video-games/1370399.htm]

*** SPOILERS ***
I finally got this quest to work, and I thought I'd share.
I was having the same problems as many other people - get to the train, either it leaves too quick, or I disarm & it blows up anyway. From what I can tell, this is the bug in the quest. That it seems like you can succeed when you've already failed the quest.
Here's how I did it successfully:
1. Sneak into the tower after the spy.
2. Wait at the bottom - eavesdropping on his conversation. The game will tell you when you've successfully eavesdropped on him - it will be right after he gives the details of the bomb over the radio.
DO NOT CONFRONT THE SPY!!
3. Immediately leave the tower, go to the monorail, and disarm the bomb.
4. See Col. Hsu AFTER disarming the bomb. Not before.

Every time before that I attacked the spy - or I went to Col. Hsu 1st. Do neither.

How did you found out the ref_id for this quest? I'm asking, cause i need the ID for an other quest, and i wasn't able to findout yet.
Thx