When I go to the "Briefing Room" and go to the briefing the go to hangar button is missing. It shows itself as a multiplayer mission and I can't play it. The only thing I've did is added an E-Wing, TIE Armageddon, Colossus and K-Wing in that order. Is this the result of adding the ships or is it something else? If it is the ships how can I fix it without removing the ships or do I have to remove the ships?

I think the problem is with the "custom" ships you have added. The files might have altered some impotant files in your XWA directory. One solution is to re install the game and NOT installing custom made files, since theese files might corrupt XWA.