Went to a customer who had setup Kerberos but the RSS Viewer Web Part was still throwing the “does not support authenticated lists” message, even though Kerberos was setup 100% correctly.
Turns out the issue was with the FQDN of the sites, they had http://portal.company.co.za as their default mapping which RSS does not seem to like, once I added an internal default mapping to point to http://portal the RSS Viewer worked 100%. So the customer still access SharePoint using http://portal.company.co.za but SharePoint communicates with http://portal.
Not sure what the exact issue is with the FQDN, suspect if might be something to do with communication between servers; will let you know when I find out.
Doug “bobTheBuilder” McCusker