Message
Feed is an obsolete version
Explanation
This document appears to be based an obsolete version of the specification.
Solution
Early adopters of the Atom format should upgrade their feed to conform to RFC 4287. For more information about Atom, please see the AtomEnabled.org web site.
If you are looking to validate an Atom 0.3 feed, this validator does not appear to have been upgraded to support Atom 1.0 yet.
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You might be able to find help in one of these fine resources.