maverick upgrade, now cannot open app store, why?

Disable anti virus softwrare if installed

Make sure the firewall is turned off in System Preferences > Security & Privacy > Firewall

Make sure Gatekeeper is enabled

Open System Preferences > Security & Privacy then select the General tab.

Make sure either Mac App Store or Mac App Store and identified developers is selected. If that area is grayed out, click the padlock icon to proceed.

OS X: About Gatekeeper