Can't open Users & Groups preference pane?

Question

I am only user on my MBA. I was going to add wife as another user, but each time I try open User and Groups in System Preferences I get:
Preference Error
Could not load Users & Groups preference pane.
I found this post on the same issue. I also recently upgraded to Mountain Lion from Snow Leopard. I tried to follow the suggestion to open via Terminal app by entering /System/Library/PreferencePanes/Accounts.prefPane, but only got response that it is a directory.
Armando

Answer 1

1. You have a corrupt user picture.
2. Read this whole message before doing anything. If you're not sure you understand it, STOP. Get someone with more experience to help you; e.g., by making a "Genius" appointment at an Apple Store.
3. Back up all data if you haven’t already done so. Before proceeding, you must be sure you can restore your system to the state it’s in now. If you don't have backups, or you don't know how to restore from them without being able to log in, STOP.
4. Triple-click anywhere in the line below on this page to select it:
/System/Library/CoreServices/Directory Utility.app
Rght-click or control-click the highlighted text and select
Services ▹ Open
from the contextual menu.* The application Directory Utility will open.
5. In the Directory Utility window, click the lock icon and authenticate. Select the Directory Editor tool in the toolbar. Select Users from the Viewing menu in the toolbar, if not already selected. Select your user account in the list. On the right is a list of properties and values. Select the property "JPEGPhoto" and delete it by clicking the minus-sign icondirectly below the property list. There are two such icons in the window. You want the one on the right, not the one on the left.
CAUTION: Do not click the minus-sign icon on the left, below the user list.
Then click the Save button in the lower right corner of the window. Quit Directory Utility.
6. Try again to open Users & Groups. If it still doesn't work, repeat the above steps with any other users you created. You'll need to reset the user pictures. Don't use the same ones.
7. Besides the users you created, there are many other items in the user list, representing built-in accounts. Don't change those accounts.
8. CAUTION: There is no "undo" in Directory Utility. If you make a mistake and delete something in the Directory Editor that should not have been deleted, restore your whole system from a backup and start over. I have no other help to offer in that case.
*If you don't see the contextual menu item, copy the selected text to the Clipboard (command-C). Open a TextEdit window and paste into it (command-V). Select the line you just pasted and continue as above.