Open the App Store on your Mac. Make sure you’re connected to a power source if you’re on a laptop. It often prompts you to do so anyway when upgrading the system, and this is a long download. You’ll want to make sure your battery doesn’t run out in the process. Click on the download button and type in your password. The download takes at least an hour, and once it moves to the installing stage it takes another thirty minutes or so before it automatically reboots your system. Once it has restarted, you’ll know that it has upgraded successfully. Some users are reporting an Error Message when they try to download Mountain Lion. One message is just asking users to simply try again, another message is designating it to be Error 100, and another was saying the distribution file could not be verified. The first solution is the easier and most obvious one. Quit the Apple Store and restart your computer. That should be the first choice of any error problem. Relaunch the Apple Store and attempt to download Mountain Lion again. Hopefully it will work and the situation will be resolved. Simply waiting it out is the second option. Often when a new software, much-anticipated app, or new device is released, Apple’s servers can get overloaded with everyone trying to get the new product at the same time. If you can wait, it will make all the difference.
If the problem persists, it’s suggested to empty the cache for the App Store. This can be done for any problem you are having with the App Store. To do this, initiate a search for the “~/Library/Caches/com.apple.appstore” folder on your hard drive, but instead of using the search box, use the “Go to Folder” from the Go menu in Finder. Once you locate it, move it to the Trash, and be sure you perform an “Empty the Trash” as well. Relaunch the App Store and initiate the download again. Getting past the error, downloading directly to your hard drive, instead of buying the upgrade on a CD, is certainly the better option. There may be some obstacles along the way, but as long as there are easy fixes such as this, it beats the prior method of upgrades.
