This demo contains complete tips that help fix An unknown error has occurred error box while trying to download/install/buy an app on Apple Store, or download a new OS X on your Mac.
Task: log out your iTunes/ Apple account temporarily and, re-log your ID in later. Troubleshooting steps are: head to the top toolbar click "Store" click "Sign Out" sign back in Other options: 1. Uninstall current iTunes using the recommended app remover PRO in this video > restart your Mac > download & install an old version of iTunes@ support.apple.com/downloads/itunes later. 2. Create a new account on your Mac > restart > try later. 3. Try Unhiding > hiding your purchases.
If you can't upgrade your Mac computer (downloading OS X)....
Solution 1: Quit App Store. Wait 10 seconds or more. (Optional) Clear cookies in Safari Open App Store again. Try again. For advanced users, try the below cmd codes: ls -la /private/var/folders/*/*/*/com.apple.appstore rm -frv /private/var/folders/*/*/*/com.apple.appstore Try downloading again. If the issue persists, try restarting your computer and attempting the app purchase again.
Solution 2: 1. Go to the Applications and delete the partially downloaded Mavericks application.
2. Return to App Store and try a fresh download.
Other options: a. try downloading OS X later. b. use a different router. c. Make sure you have downloaded all the latest system updates.