on my game i did the kings quest and got them to lay off the NCR, then the NCR ambassador asked me to go see cl moore.. i did some quests after and changed my armor (previous post) and said i was now not liked by NCR and quest "for the republic" became discoloured on my list. so i boosted my liking up so i cld do the quest... however the quest is still discoloured and the ambassador + moore are no where to be seen. please tell me this isnt a bug!

It certainly seems so. 

If you're playing on PC I'd use the console.

lame.

I have had the exact same problem. At first i thought i had killed an NCR member or something but i hadn't so i try everything but nothing seem to work apart from...(and your not going to like this) making a new character and be EXTREMELY careful what you do around the NCR .

Did you change into faction specific armor???

yeh i did... sucks just given u for a bit then ill start again when the hurting stops :(.... fun game tho!