I'm on the quest "You'll Know When it Happens" at the Hoover Dam and the objective right now is to report to Ranger Grant in the Visitor's Center. Well when I go to talk to him, my only dialogue option is "Goodbye"

This is definitely a bug because it was reported on the Fallout Wiki saying it occurs if you do quests for independent, Mr. House, and then switch to NCR towards the end. At least I think that's what it said. It's since been removed off the wiki by some random person.

Is there any way I can fix this?

I have the same problem. I also can't complete "Restoring Honor", after taking Nelson, Polatli doesn't have anything to say to me.

Maybe buy the game?

I frequent the Vault, and haven't seen any note pertaining this issue..

Maybe stop making stupid assumptions and thank me for not reporting you.

http://img253.imageshack.us/img253/5760/fnvsteam.jpg

well, thank you for your steam ID, not sure what i should be doing with it though.. nice gesture none the less.

I'm sorry, do people in whatever society you come from not take offence when being accused of stealing ?

Not really, no. Innocent until proven guilty and all that. You've gotta learn to shrug things off tbh.

Anyway... any help would be appreciated, I am basically stuck in the game at this point.