A user posted this on the microsoft.public.mac.office
SharePoint needs to have its 'Client Integration' feature turned on. Log in to your SharePoint Central Administration site as an administrator. Navigate to Central Administration > Application Management > Authentication Providers then click the appropriate zone (in my case, 'Default'). If 'Enable Client Integration' is set to No, switch it to Yes and click Save.
Let us know if this works for you.

Comments (1)
Posted on the Office newsgroup by jaime_sf
Gutch's solution solved my issue in a round about way. While in the authentication management area, i noted the url as http://sharepointserver_nonfqdn:5280/
When I used the non fqdn, it worked.