Are you using Internet Explorer. There has been problems in the past with the app mart and IE. Try Firefox, even if you delete it right after you have downloaded the apps you want like I did.
CAR: 2007 G35 Sport Coupe 5AT
HARDWARE: Dell D630 w/ dock, internal 80G HD, internal 320G HD, Verizon Wireless Card, iBlue GM-2 GPS w/iGuidance, OBDPros w/DashCommand, Visteon HD Radio w/ Home Made Cable, Current Version of RR w/ DFX Skin. My Install.