Troubleshooting has been performed by some users by executing the action of quitting and relaunching the App Store while others took drastic measures by putting there devices into Safe Mode which to no avail.
Here are some work around for you guys to test if it will help resolve the problem:
1. You have to be sure that if you have Anti-Virus installed on your device to either un-install or temporarily deactivate the application.
2. Clear out the Cache and Cookies being used by the Mac App Store.
Apple-Care already responded to some of the queries of those affected by this problem and they recommended that the completion of the installation would require at least 48-72 hours.