Set ATHENA.MIT.EDU realm as default for Kerberos credentials

I am getting an error when trying to launch SAPgui. My Kerberos tickets are set to use a realm other than ATHENA.MIT.EDU as the default, such as CSAIL.MIT.EDU, MEDIA.MIT.EDU, ALUM.MIT.EDU. I have verified that I don't have any other applications that need the other realm Kerberos tickets as the default. How can I set ATHENA.MIT.EDU as the default realm for my Kerberos credentials?

Windows

These instructions are for Kerberos for Windows 3.2.2. Instructions for other Kerberos versions may vary to some degree.

1. From the All Programs menu, launch the Network Identity Manager by following the path:
   All Programs > Kerberos for Windows > MIT Kerberos Ticket Manager.
2. Click Get Ticket and ensure that the principal is your username followed by @ATHENA.MIT.EDU.
3. Enter your password and select OK to get new Kerberos tickets.
4. Highlight the ATHENA.MIT.EDU credentials and click Make default.
5. Close the Ticket Manager.

Macintosh

1. Launch Ticket Viewer
2. Click "Add Identity"
3. In the new window, enter <username>@ATHENA.MIT.EDU in the Identity field, and enter your password. Click Continue.
4. When the new ticket appears in your list, select it, then click the "Set as Default" button.

For more detailed information, see Kerberos Preferences on Mac OS X, which describes various ways to configure Kerberos on the Mac.