Users can't access iCal Server without adminstrator privileges

I have just installed Apple's Snow Leopard Server, Version 10.6.8. Everything installed just great and with one exception works fine.

ICal is running on the server. When a client attempts to access the server he is denied unless he has administrator privileges. For example:

I open iCal and select "Accounts". I click the + button and for the account type I select "CalDav". I enter a User Name and Password. Then the server address. An error message comes back that states “No CalDav servers were found for [our server address]"

However, I can then open the Workgroup Manager and give that same user administrator access by checking the check box that states "User Can Administer This Server" and repeat the above process and everything works fine.

Any ideas are appreciated.