Thanks for the reply pal
I'll try that solution and get back to you if it works
Yes, having the game update for New Vegas is essential to running Dead Money. As suggested though, I'd advise completely removing the DLC content first and then re-download (you don't get charged again).
You can also trying clearing the game cache (different than the system cache) by holding RB, LB, and X at the same time when the game boots up.