Forza 4 Motorsport help! How do you install content disc (disc 2)?

Started playing essentials edition, couldn't get the car packs through the marketplace. Found out they had been taken off, so I bought a 2 disc copy off of ebay (Legit set, disc 1 has disclaimer about not being labeled for individual sale). 4 GB 360, have installed disc 1 to 16 gb flash drive. Still have lots of room on flash drive. Try loading disc 2, get message asking me to insert disc 1.

Do I need to erase my prev. save from the basic edition I started with? Can I install content and still use beginning save with it?