[Rook]

Yes, I get that a username and pass is needed... I think we're getting off track assuming I have any projects open or resources assigned with email addresses that need to correspond to anything. To clarify, this is at the app settings level. No resources on projects come into play at all. Fuggedabout 'em.

As in:
No documents (project plans) open, no resources with email addresses considered. In fact, for the purposes of this, we can assume this is a fresh install.

OmniPlan -> Preferences... -> Accounts
Account Type: CalDAV
User: [some regular user that has an account & a calendar on following server]
Password: [password for the user's account]
Server address: server.domain.com
Port: 443 / SSL checked (cert is valid)

Click Test -> Checking account... -> unauthorized

If the user and pass just need to be for a user with an account on the server and CalDAV services are running on that server, address is right / port is OK, that should work... no?