Help for Error 13
Quit the App Store if it's open then open the Finder.
From the Finder menu bar click Go > Go to Folder
Type or copy / paste: ~/Library/Cookies
Click Go then move the com.apple.appstore.cookies file to the Trash.
Relaunch the App Store.
If that doesn't help, type or copy / paste: ~/Library/Preferences/com.apple.appstore.plist
Click Go then move the com.apple.appstore.plist file to the Trash.
Relaunch the App Store.