Since I've started playing, the NCR & the NCR Rangers are extremely hostile toward me, even Cass shoots me when I go to the NCR compound.
Is this a glitch or have I done something in my travels to irritate them?

your probably wearing clothes from a faction that ncr hates for example powder gangers or legion

Thankyou for your response, I'm actually wearing NCR armor, I've even stripped down to my undergarments and they still attack me...

Sometimes the game forgets to notice when you change out of faction armor. This happened to me and I had to put on legion armor and take it off so that it said "you are no loner disguised as a legion member."

my friend, this is a [censored] glitch i promise you. i am idolized by the NCR, yet when i use their radio to call for support, the damn trooper attacks me, whether i am in standard combat armor or my [censored] underwear. this has also been happening to me at many NCR camps, despite my flawless rep with them. it is a game breaking bug, because i am now unable to finish many side quests as well as the main quest. it's a glitch, and one that should never have been there to begin with, if Bethesda had properly tested the damn game before releasing it. i am truly sorry that you are having this problem, as this bug can seriously piss all over many of the quests available to you in the game. all we can hope for is this so called "patch" that is apparently coming within the next few weeks according to Bethesda, although i would not be surprised if we end up waiting months for this patch. a patch we shouldn't even need, if they had done their jobs properly to begin with.

Great, looks like I will have to start again, my PS3 isn't connected to the internet so a patch is no good to me. There's actually 2 side quest's I cant complete, bringing Cass to get murdered & the Mission with the Powergangers for the NCR, the troops shoot me, but the NCR President talks to me... friken weird. Oh well, will return game and wait for a newer bug free version to be released. with enough returns Bethesda should get the message, but then again, they didn't with Fallout 3 GOTY.

NCR idolizes me as well, but when in Freeside the NCR MP always shoot at me.Not I can run up to them and start a conversation with them if I can get close enough without them running off. Nowhere else do they shoot at me, however I can note it started as soon as I wiped out the King and all of his gang for the NCR...