App store crashes when I try to download mountain lion.

Hello Margot.L,

I was looking through our documentation about things you may be able to do to troubleshoot the issue. Here is an article about troubleshooting an issue with softare on the Mac named Mac OS X: How to troubleshoot a software issue found here http://support.apple.com/kb/HT1199.

1. The first and easiest test to try is to see if the issue affects a different user account on your Mac. Each user account has customized preferences and other items stored in its home directory. You'll first need to create an additional user if one does not already exist (follow steps a-h below). Then, log out of the current user and test the issue in the new user account.If this resolves the issue, there may be an issue with a file in the home directory of the original user account.
   1. From the Apple menu, choose System Preferences.
   2. From the View menu, choose Accounts (or choose Users if using Mac OS X v10.2 or earlier).
   3. Click "+" (or click New User if using Mac OS X v10.2 or earlier).
   4. Give the new user a name and short name.
   5. Mac OS X v10.3 or earlier only: Click the Password tab, and give the user a password.
   6. Mac OS X v10.3 or earlier only: Click Security.
   7. Select the checkbox for "Allow user to administer this computer". This makes the user account an administrator.
   8. Click OK, or quit System Preferences.
2. Start up in Safe Mode (Mac OS X v10.2 or later only). If the issue does not occur, there may be an issue with a startup item, login item, or kext file. Refer to this article for troubleshooting suggestions.
3. If the issue does not appear to be related to preferences, a login item, or a kext file, and still persists in Safe Mode, there may be an issue with a cache file in your home folder:
   
   1. From the Finder's Go menu, choose Home.
   2. Open the Library folder.
   3. Drag the Caches folder to the desktop.
   4. Attempt to reproduce the issue.
   5. If issue is resolved, drag the Caches folder to the Trash.
   6. If issue persists, from the Finder's Go menu, choose Go To Folder.
   7. Go to this folder: /Library
   8. Drag the Caches folder to the desktop.
   9. Attempt to reproduce the issue.
   10. If issue is resolved, drag the Caches folder to the Trash.

Cheers,

Sterling