I'm doing the quest "I put a spell on you" for the Legion, som I'm supposed to plant the explosive charge (not defuse it, like you do with the NCR quest).

I'm at the monorail, after I snuk past the guards. Now I see the monorail, but I can only press A and travel to the strip. I can't physically enter the monorail to plant the explosives, and complete the quest! Anybody know anything about this? Experienced the same? Any alternative ways of planting the explosive?

You may need to talk to a certian NPC somewhere for it to occur, I don't know though since when I finished this (In NCRs favor) the quest went off without a hitch.