java.lang.IllegalStateException: mutations cannot occur on nodes already added to a tree
        at org.netbeans.modules.xml.xdm.nodes.NodeImpl.checkNotInTree(NodeImpl.java:207)
        at org.netbeans.modules.xml.xdm.nodes.Element.setTagName(Element.java:117)
        at org.netbeans.modules.xml.xdm.nodes.Element.setPrefix(Element.java:151)
        at org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.fixupPrefix(AbstractDocumentComponent.java:581)
        at org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.appendChildQuietly(AbstractDocumentComponent.java:286)
        at org.netbeans.modules.xml.xam.dom.AbstractDocumentComponent.appendChildQuietly(AbstractDocumentComponent.java:74)
        at org.netbeans.modules.xml.xam.AbstractComponent._appendChildQuietly(AbstractComponent.java:111)
        at org.netbeans.modules.xml.xam.AbstractComponent.appendChild(AbstractComponent.java:315)
        at org.netbeans.modules.xml.schema.model.impl.SchemaImpl.addElement(SchemaImpl.java:122)
        at org.netbeans.modules.websvc.design.schema2java.OperationGeneratorHelper.addInputMessageToOperation(OperationGeneratorHelper.java:342)
        at org.netbeans.modules.websvc.design.schema2java.OperationGeneratorHelper.addWsOperation(OperationGeneratorHelper.java:172)
        at org.netbeans.modules.websvc.design.view.actions.AddOperationAction.addWSDLOperation(AddOperationAction.java:219)
        at org.netbeans.modules.websvc.design.view.actions.AddOperationAction.access$000(AddOperationAction.java:92)
        at org.netbeans.modules.websvc.design.view.actions.AddOperationAction$1$1.run(AddOperationAction.java:145)
        at org.openide.util.Task.run(Task.java:244)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:561)
        at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:986)