Call of the Dead Question?

I am currently playing Call of the Dead in Black Ops right now. I have four perks, Quick Revive, Juggernaut, PHD Flopper, and Sleight of Hand (bought in that order). For some reason, I can't buy anymore perks! I have walked up to Dead shot Daiquiri and Stamin-Up and I tried to buy both perks, and it just makes a sound like the machine is broken. Please help me resolve this with a solution soon, I can't wait forever. Also, 10 points if someone tells me if Double Tap is on the map or not.