Originally Posted by Brian

Buzdjow - have you ever had a different username or password for the server you're syncing with now? Or did you just set up the account for the first time before syncing?

One of our theories is that the Calendar application is showing the login panel, but then pulling old/obsolete login information from the phone's keychain and sending that to the server instead of what you typed.

If you're willing to set up a test account with one of the other sync providers listed here (one you've never used before), it would be useful to know if the problem is linked to setting up sync on a specific server, or if it prevents you from setting up sync with any server.