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I have received this message for many feeds which are read without problem by other products eg Opera.
As I have not found equivalent functionality elsewhere I have persisted with Feedreader and I now have a solution:
Paste the feed link into Feed Validator (at http://feedvalidator.org/\).
This reports any errors in the feed but more importantly it changes the link itself.
Copy and paste the new feed link back into the feed properties and update the feed
The feeds that caused me problems start feed:// ; these are changed to http:// .