10.9.2 Mavericks Calendar.app // Invites Not Sending

I have a user who only has local "On My Mac" calendars in Calendar.app. He can receive and accecpt invitations. He can create events. However, when adding invitees, the invite is not sent by the user, and thusly not received by the invitee.

I have:

Restarted

Repaired Permissions

Removed Calendar Caches

Removed associated plist files in ~/Library/Preferences

Removed ~/Library/Containers/com.apple.iCal

Removed all calendars (after archiving them) and tested sending an invite from a fresh calendar with no other events in it.

Removed Mail.app preferences.

None of this has worked.

I even synced all of his calendars to Google Apps and attempted to send an invite from the Google synced calendar in Calendar.app to no avail. He can send invites on iPhone, and from Google Celendar Web UI, but not from 10.9.2 Calendar.app.

Any suggetions?

I have not:

Removed and re-installed his IMAP account.

I do not want to rebuild his user account from scratch.

Thank you,

Jeremy