org.xml.sax.SAXParseException; cvc-complex-type.2.4.a: Invalid content was found starting with element 'compilation-unit'. One of '{"http://www.netbeans.org/ns/freeform-project-java/2":compilation-unit}' 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 'compilation-unit'. One of '{"http://www.netbeans.org/ns/freeform-project-java/2":compilation-unit}' 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$6.run(ProjectManager.java:671)
   at org.openide.util.Mutex.writeAccess(Mutex.java:438)
   at org.netbeans.api.project.ProjectManager.saveProject(ProjectManager.java:671)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener.saveModifiedProject(CustomizerDialog.java:370)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener.access$500(CustomizerDialog.java:253)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1$1.run(CustomizerDialog.java:318)
   at org.openide.filesystems.FileUtil$2.run(FileUtil.java:431)
   at org.openide.filesystems.EventControl.runAtomicAction(EventControl.java:127)
   at org.openide.filesystems.FileSystem.runAtomicAction(FileSystem.java:609)
   at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:415)
   at org.openide.filesystems.FileUtil.runAtomicAction(FileUtil.java:435)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2$1.run(CustomizerDialog.java:309)
   at org.openide.util.Mutex.writeAccess(Mutex.java:399)
   at org.netbeans.modules.project.uiapi.CustomizerDialog$OptionListener$2.run(CustomizerDialog.java:306)
   at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1432)
   at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2042)