Message
Unable to validate namespace: http://namespace.uri/. See the foo specification at http://namespace.uri/specification
Explanation
Even though the feed validator has build in support for quite a large number of popular namespaces, you somehow managed to have found one that the feed validator does not (yet) support.
Solution
The feed validator is unable to verify the correct usage of this namespace. Either it is not well-specified, there are no test cases to demonstrate correct use or it just hasn't been implemented.
Please consult the specification for correct use of this namespace.
If you know of a namespace that you feel that the feed validator should support, let us know. Please include in your request a pointer to the documentation for the namespace. Such documentation should describe the XML elements and attributes defined for this namespace. More information and the status of current requests can be found on the wiki.
Not clear? Disagree?
You might be able to find help in one of these fine resources.
