Ok, so i'm massively stuck.

Ive played through this quest, and it seems like i have completed it. I've done all his errands, and i persuaded the NCR officer to use Contreas to catch others, rather then arresting him (the barter-80 + caps 250 option)

Now the only dialogue option for the NCR officer is "Goodbye", and Contreas and the security Officer at Mcarren Airbase just speak to me asif nothing has happened.

What have i done wrong? and is there anyway i can fix this?

Please help,

Yes this happened to me too. The only way to getthe option from Contreras to get This Machine is to kill the NCR guy. But dont worry, Nobody turns hostile and killing him wont hurt your reputation.

Thanks mate
Was starting to think nobody would reply to this.

I've had a problem even getting this quest to start. I tried talking to him while in the process of doing the interrogation quest, which turns out to be a bad idea as he does not have the relevant dialogue option if you do that. Next character I tried talking to him before anyone else at McCarran, and still nothing. Is there a specific point at which you should ask him about it? The wiki had nothing on getting the quest started other than the warning about doing so while doing the interrogation quest.

I was able to finish this, only after I hacked Contreras PC on the second floor, The quest is bugged, so I cheated and hacked his PC, I didn't have enough science points. When you hack it, there is a message, download it and go straight to Boyd or whatever her name is and tell her. Well this is the workaround if you want to get rid of him.

I faced the same problem. First time talk to him there are no dialogue options to start the quest. I tried again the second time and presto the dialogue for the quest opens us. This was mentioned in the wiki under the topic This Machine or the Quest it self. It was mentioned.