first, try checking the validator’s help:
“Message
An item should not include both foo and bar
Explanation
This item contains two elements which mean the same thing. This can occur in RSS 2.0 when you mix core elements and namespace elements. This can confuse news aggregators and RSS parsers, since there are no universally accepted rules about which element takes precedence.
Examples of item elements that mean the same thing:
author and dc:creator
category and dc:subject
source and dc:source
Solution
Remove one of the duplicate elements.”
so that means that you either remove line 23 (that has all the dc:source stuff), or you remove all the <category>blah</category> stuff.
