Error In Starting of Mule App

Some times Mule app failed to start , throwing weird exception like this :

org.xml.sax.SAXParseException: cvc-elt.1: Cannot find the declaration of element 'mule'.
        at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
        at org.apache.xerces.util.ErrorHandlerWrapper.error(Unknown Source)
        at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
        at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
        at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)
        at org.apache.xerces.impl.xs.XMLSchemaValidator.handleStartElement(Unknown Source)
        at org.apache.xerces.impl.xs.XMLSchemaValidator.startElement(Unknown Source)
        at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(Unknown Source)
        at org.apache.xerces.impl.XMLNSDocumentScannerImpl$NSContentDispatcher.scanRootElementHook(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
        at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
        at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
        at org.apache.xerces.parsers.DOMParser.parse(Unknown Source)
        at org.apache.xerces.jaxp.DocumentBuilderImpl.parse(Unknown Source)
        at org.springframework.beans.factory.xml.DefaultDocumentLoader.loadDocument(DefaultDocumentLoader.java:75)
        at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:388)
        at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:334)
        at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:302)
        at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:174)
        at org.mule.config.spring.MuleApplicationContext.loadBeanDefinitions(MuleApplicationContext.java:113)
        at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:130)
        at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:537)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:451)
        at org.mule.config.spring.SpringRegistry.doInitialise(SpringRegistry.java:89)
        at org.mule.registry.AbstractRegistry.initialise(AbstractRegistry.java:109)
        at org.mule.config.spring.SpringXmlConfigurationBuilder.createSpringRegistry(SpringXmlConfigurationBuilder.java:119)
        at org.mule.config.spring.SpringXmlConfigurationBuilder.doConfigure(SpringXmlConfigurationBuilder.java:73)
        at org.mule.config.builders.AbstractConfigurationBuilder.configure(AbstractConfigurationBuilder.java:46)
        at org.mule.config.builders.AbstractResourceConfigurationBuilder.configure(AbstractResourceConfigurationBuilder.java:78)
        at org.mule.config.builders.AutoConfigurationBuilder.autoConfigure(AutoConfigurationBuilder.java:101)
        at org.mule.config.builders.AutoConfigurationBuilder.doConfigure(AutoConfigurationBuilder.java:57)
        at org.mule.config.builders.AbstractConfigurationBuilder.configure(AbstractConfigurationBuilder.java:46)
        at org.mule.config.builders.AbstractResourceConfigurationBuilder.configure(AbstractResourceConfigurationBuilder.java:78)
        at org.mule.context.DefaultMuleContextFactory.createMuleContext(DefaultMuleContextFactory.java:84)
        at org.mule.module.launcher.application.DefaultMuleApplication.init(DefaultMuleApplication.java:207)
        at org.mule.module.launcher.application.ApplicationWrapper.init(ApplicationWrapper.java:64)
        at org.mule.module.launcher.DefaultMuleDeployer.deploy(DefaultMuleDeployer.java:47)
        at org.mule.module.launcher.MuleDeploymentService.guardedDeploy(MuleDeploymentService.java:420)
        at org.mule.module.launcher.MuleDeploymentService.start(MuleDeploymentService.java:186)
        at org.mule.module.launcher.MuleContainer.start(MuleContainer.java:160)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.mule.module.reboot.MuleContainerWrapper.start(MuleContainerWrapper.java:56)
        at org.tanukisoftware.wrapper.WrapperManager$12.run(WrapperManager.java:2788)
[28/01/2015 18:17:07 INFO  DefaultMuleApplication:197] App 'plum-slice-rest-api-3.3.4-SNAPSHOT' never started, nothing to dispose of
ERROR 2015-01-28 18:17:07,426 [WrapperListener_start_runner] org.mule.module.launcher.MuleDeploymentService:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ Failed to deploy app                                     +
+ 'test', see below          +

The solution which you can try in this case pretty simple .Just delete .mule folderPost Comments and Suggestions !!