I was having a running Solr 4.1 on Windows Server 2008 R2. The Solr is deployed on Tomcat. However, today it stops suddenly, and while accessing Solr it gives following error.

HTTP Status 503 - Server is shutting down

type Status report

message Server is shutting down

description The requested service is not currently available.

On further looking into Logs, we got following:

Log File: tomcat7-stderr.2013-05-09.txt

    May 09, 2013 8:00:40 PM org.apache.solr.core.CoreContainer finalize
    SEVERE: CoreContainer was not shutdown prior to finalize(), indicates a bug -- POSSIBLE RESOURCE LEAK!!!  instance=2221663

Log File: catalina.2013-05-09.txt

May 09, 2013 7:59:25 PM org.apache.solr.core.SolrResourceLoader <init>
INFO: new SolrResourceLoader for directory: 'c:\solrdir\'
May 09, 2013 7:59:29 PM org.apache.solr.common.SolrException log
SEVERE: Exception during parsing file: null:org.xml.sax.SAXParseException; systemId: file:/c:/solr/solr.xml; lineNumber: 2; columnNumber: 6; The processing instruction target matching "[xX][mM][lL]" is not allowed.
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPIData(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanPIData(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPI(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
    at org.apache.solr.core.Config.<init>(Config.java:121)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:428)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:404)
    at org.apache.solr.core.CoreContainer$Initializer.initialize(CoreContainer.java:336)
    at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:98)
    at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:281)
    at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:262)
    at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:107)
    at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4656)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5309)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633)
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:977)
    at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1655)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

May 09, 2013 7:59:29 PM org.apache.solr.servlet.SolrDispatchFilter init
SEVERE: Could not start Solr. Check solr/home property and the logs
May 09, 2013 7:59:29 PM org.apache.solr.common.SolrException log
SEVERE: null:org.apache.solr.common.SolrException: 
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:431)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:404)
    at org.apache.solr.core.CoreContainer$Initializer.initialize(CoreContainer.java:336)
    at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:98)
    at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:281)
    at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:262)
    at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:107)
    at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4656)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5309)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633)
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:977)
    at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1655)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.xml.sax.SAXParseException; systemId: file:/c:/solrdir/solr.xml; lineNumber: 2; columnNumber: 6; The processing instruction target matching "[xX][mM][lL]" is not allowed.
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPIData(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanPIData(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPI(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
    at org.apache.solr.core.Config.<init>(Config.java:121)
    at org.apache.solr.core.CoreContainer.load(CoreContainer.java:428)
    ... 20 more

May 09, 2013 7:59:29 PM org.apache.solr.servlet.SolrDispatchFilter init
INFO: SolrDispatchFilter.init() done
May 09, 2013 7:59:29 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\docs
May 09, 2013 7:59:30 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\manager
May 09, 2013 7:59:30 PM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\ROOT
May 09, 2013 7:59:30 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8983"]
May 09, 2013 7:59:30 PM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["ajp-bio-8009"]
May 09, 2013 7:59:30 PM org.apache.catalina.startup.Catalina start
INFO: Server startup in 9578 ms
May 09, 2013 8:00:40 PM org.apache.solr.core.CoreContainer finalize
SEVERE: CoreContainer was not shutdown prior to finalize(), indicates a bug -- POSSIBLE RESOURCE LEAK!!!  instance=2221663

Any idea what could be wrong and how to fix?