Writing the JBossAS 7 standalone.xml the following is reported for subsystems with no content: -

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09:56:51,828 ERROR [stderr] (pool-2-thread-1) Caused by: javax.xml.stream.XMLStreamException: xmlns has been already bound to urn:jboss:domain:remoting:1.0. Rebinding it to urn:jboss:domain:naming:1.0 is an error
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09:56:51,829 ERROR [stderr] (pool-2-thread-1) at com.sun.xml.internal.stream.writers.XMLStreamWriterImpl.writeDefaultNamespace(XMLStreamWriterImpl.java:775)
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09:56:51,829 ERROR [stderr] (pool-2-thread-1) at com.sun.xml.internal.stream.writers.XMLStreamWriterImpl.writeNamespace(XMLStreamWriterImpl.java:992)
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09:56:51,829 ERROR [stderr] (pool-2-thread-1) at org.jboss.staxmapper.FormattingXMLStreamWriter$13.run(FormattingXMLStreamWriter.java:300)

This error is caused because the attribute queue is not called before a subsequent call to setDefaultNamespace, after setDefaultNamespace the writeNamespace operations in the queue are no longer valid.