Contacts crash caused by NSException error

If you are using Outlook or Entourage:

1) On some versions of Office, there is a Database rebuild program. You may be able to use that to fix it. Alternatively, you could export your contacts and only reimport the most important after deleting all of them. vCards can be used by Apple's Addressbook program. Alternatively, you can try to catalog all your attachments separate from Outlook. And you can make an effort to export and detach the largest attachments in your email. This will help make the database less problematic for rebuild. And since you say your program will not stay open, it probably is best to simple open it with the internet turned off, or booting in safe mode with the Shift key selected.

2) Upgrading to Yosemite will not repair the problem. It is likely your database has gotten corrupt.

If you are using the built-in Apple Mail capability for Exchange, and remember your password, com.apple.mail.plist can be removed, and you can recreate your settings from scratch. Backup any locally stored e-mails before proceeding. Those are using in Users -> your name -> Library -> Mail and Users -> your name -> Library -> Mail Downloads.