Hi there!
It appears that you have an external version of MagpieRSS installed in your WP-blog, since rss_fetch.inc is not a default WP file. Is that on purpose (to support some ancient plugin) or have you just not upgraded since >1.5 or not removed the wp-includes directory prior to upgrade?
Since WP 1.5, most of the MagpieRSS functionality has been embedded in WP. However, some ancient plugins may still require the standalone MagpieRSS application to be installed to function. One of the initial Delicious-plugins was like that I think. Try finding a newer plugin with the same functionality if that is the case.
When you know you’re not depending on the external MagpieRSS functionality anymore, upgrade to the latest WP version by following the upgrade instructions. These will tell you to remove the directories wp-includes and wp-admin, and that should remove the external MagpieRSS application in the process.
OK