org.xml.sax.SAXParseException; cvc-complex-type.2.4.a: Invalid content was found starting with element 'explicit-platform'. One of '{"http://www.netbeans.org/ns/j2se-project/3":web-service-clients, "http://www.netbeans.org/ns/j2se-project/3":source-roots}' is expected.
   at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:0)
   at org.apache.xerces.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:0)
   at org.apache.xerces.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:0)
   at org.apache.xerces.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:0)
   at org.apache.xerces.impl.xs.XMLSchemaValidator$XSIErrorReporter.reportError(XMLSchemaValidator.java:0)
   at org.apache.xerces.impl.xs.XMLSchemaValidator.reportSchemaError(XMLSchemaValidator.java:0)
   at org.apache.xerces.impl.xs.XMLSchemaValidator.handleStartElement(XMLSchemaValidator.java:0)
   at org.apache.xerces.impl.xs.XMLSchemaValidator.startElement(XMLSchemaValidator.java:0)
   at org.apache.xerces.jaxp.validation.DOMValidatorHelper.beginNode(DOMValidatorHelper.java:0)
   at org.apache.xerces.jaxp.validation.DOMValidatorHelper.validate(DOMValidatorHelper.java:0)
   at org.apache.xerces.jaxp.validation.DOMValidatorHelper.validate(DOMValidatorHelper.java:0)
   at org.apache.xerces.jaxp.validation.ValidatorImpl.validate(ValidatorImpl.java:0)
   at javax.xml.validation.Validator.validate(Validator.java:124)
   at org.openide.xml.XMLUtil.validate(XMLUtil.java:522)
   at org.netbeans.modules.project.ant.ProjectXMLCatalogReader.validate(ProjectXMLCatalogReader.java:149)
Caused: java.io.IOException: cvc-complex-type.2.4.a: Invalid content was found starting with element 'explicit-platform'. One of '{"http://www.netbeans.org/ns/j2se-project/3":web-service-clients, "http://www.netbeans.org/ns/j2se-project/3":source-roots}' is expected.
   at org.netbeans.spi.project.support.ant.AntProjectHelper.saveXml(AntProjectHelper.java:343)
   at org.netbeans.spi.project.support.ant.AntProjectHelper.save(AntProjectHelper.java:624)
   at org.netbeans.spi.project.support.ant.AntProjectHelper.access$100(AntProjectHelper.java:113)
   at org.netbeans.spi.project.support.ant.AntProjectHelper$1.save(AntProjectHelper.java:151)
   at org.netbeans.modules.project.ant.AntBasedProjectFactorySingleton.saveProject(AntBasedProjectFactorySingleton.java:426)
   at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:681)
   at org.netbeans.api.project.ProjectManager$6.run(ProjectManager.java:671)
   at org.openide.util.Mutex.writeAccess(Mutex.java:438)
   at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:671)
   at org.netbeans.modules.java.project.ProjectProblemsProviders$SourceTargetResolver$1.call(ProjectProblemsProviders.java:941)
   at org.netbeans.modules.java.project.ProjectProblemsProviders$SourceTargetResolver$1.call(ProjectProblemsProviders.java:919)
   at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
   at java.util.concurrent.FutureTask.run(FutureTask.java:166)
Caused: java.util.concurrent.ExecutionException: java.io.IOException: cvc-complex-type.2.4.a: Invalid content was found starting with element 'explicit-platform'. One of '{"http://www.netbeans.org/ns/j2se-project/3":web-service-clients, "http://www.netbeans.org/ns/j2se-project/3":source-roots}' is expected.
   at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:252)
   at java.util.concurrent.FutureTask.get(FutureTask.java:111)
   at org.netbeans.modules.project.ui.problems.BrokenReferencesCustomizer$4.run(BrokenReferencesCustomizer.java:232)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1432)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2042)