The RSS feed could be requiring authentication. Try to make sure you are logged out from that site and then paste the URL into your browser to see if it still works.
Clear cache first after your log out
If it isn't protected, then maybe there's a bug ;P
iMac i7 27"
DS1010+ [1.67GHz, Dual Core, 1GB RAM, DSM 4.0 2166] - Media server, File server, TM target, Web App Hosting
DS409+ [1.06GHz, 512MB RAM, DSM 3.1 1594] - E-Mail server and rsnapshot target for TS-439 Pro, SVN Server.
DS409+ [1.06GHz, 512MB RAM, DSM 3.1 1594] - Off-site backup target
DS107e [266 MHz, 32MB RAM, DSM none] - Collecting dust
Qnap TS-439 Pro - File server
Mac Mini Server
Boxee Box by D-Link