2461897 - Upgrade fails with error "Content is not allowed in prolog"

During the upgrade the SUM stops with error, and in the defaultTrace_XX.X.trc log (located at /usr/sap/<SID>/<InstID>/j2ee/cluster/serverX/log/) you see an exception like the one below:

#2.0#<timestamp>#0-400#Error#com.sap.engine.services.dc.cm.deploy.impl#com.sap.#BC-JAS-DPL#tc~bl~deploy_controller#C000093F43BD002000008BAD034E0086#303164850000000003##com.sap.engine.services.dc.cm.deploy.impl#J2EE_ADMIN#1##FD959D93FCAB14B283DEC96D3F4D4C3F#fd959d93fcab14b283dec96d3f4d4c3f##0#Thread[RMI/IIOP Worker [3],5,Dedicated_Application_Thread]#Plain##
An error occurred while restarting the server.
[EXCEPTION]
com.sap.engine.services.dc.cm.deploy.DeploymentException: An error occurred while restarting the server.
at com.sap.engine.services.dc.cm.deploy.impl.OfflineDeployPostProcessor.postProcess(OfflineDeployPostProcessor.java:113)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImpl.doPostProcessing(DeployerImpl.java:1135)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImpl.performDeploy(DeployerImpl.java:1024)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImpl.doDeploy(DeployerImpl.java:819)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImpl.deployInternal(DeployerImpl.java:454)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImpl.deploy(DeployerImpl.java:228)
at com.sap.engine.services.dc.cm.deploy.impl.DeployerImplp4_Skel.dispatch(DeployerImplp4_Skel.java:910)
at com.sap.engine.services.rmi_p4.DispatchImpl._runInternal(DispatchImpl.java:482)
at com.sap.engine.services.rmi_p4.server.ServerDispatchImpl.run(ServerDispatchImpl.java:81)
at com.sap.engine.services.rmi_p4.P4Message.process(P4Message.java:72)
at com.sap.engine.services.rmi_p4.P4Message.execute(P4Message.java:43)
at com.sap.engine.services.cross.fca.FCAConnectorImpl.executeRequest(FCAConnectorImpl.java:1055)
at com.sap.engine.services.rmi_p4.P4Message.process(P4Message.java:59)
at com.sap.engine.services.cross.fca.MessageReader.run(MessageReader.java:55)
at com.sap.engine.core.thread.execution.Executable.run(Executable.java:122)
at com.sap.engine.core.thread.execution.Executable.run(Executable.java:101)
at com.sap.engine.core.thread.execution.CentralExecutor$SingleThread.run(CentralExecutor.java:328)
Caused by: com.sap.engine.services.dc.cm.server.spi.RestartServerService$RestartServerServiceException: [ERROR CODE DPL.DC.3154] An error occurred while restarting the AS Java Cluster.
at com.sap.engine.services.dc.cm.server.impl.AbstractRestartServerService.restart(AbstractRestartServerService.java:214)
at com.sap.engine.services.dc.cm.server.impl.AbstractRestartServerService.restartInSafeMode(AbstractRestartServerService.java:112)
at com.sap.engine.services.dc.cm.deploy.impl.OfflineDeployPostProcessor.postProcess(OfflineDeployPostProcessor.java:105)
... 16 more
Caused by: com.sap.engine.services.dc.jstartup.JStartupException: [ERROR CODE DPL.DC.3312] An error occurred while restarting the cluster using SAP control webservice on URI [ http://<host>:5XX13/?wsdl].
at com.sap.engine.services.dc.jstartup.impl.JStartupClusterManagerImpl.restartCluster(JStartupClusterManagerImpl.java:213)
at com.sap.engine.services.dc.cm.server.impl.AbstractRestartServerService.restart(AbstractRestartServerService.java:202)
... 18 more
Caused by: javax.xml.ws.WebServiceException: com.sap.engine.services.webservices.espbase.wsdl.exceptions.WSDLException: Content is not allowed in prolog.
at com.sap.engine.services.webservices.espbase.client.jaxws.core.SAPServiceDelegate.loadWSDLDefinitions(SAPServiceDelegate.java:222)
at com.sap.engine.services.webservices.espbase.client.jaxws.core.SAPServiceDelegate. <init>(SAPServiceDelegate.java:128)
at com.sap.engine.services.webservices.espbase.client.jaxws.cts.CTSProvider.createDelegate(CTSProvider.java:179)
at com.sap.engine.services.webservices.espbase.client.jaxws.cts.CTSProvider.createServiceDelegate(CTSProvider.java:160)
at javax.xml.ws.Service.<init>(Service.java:56)
at com.sap.engine.services.dc.jstartup.ws.SAPControl.<init>(SAPControl.java:16)
at com.sap.engine.services.dc.jstartup.impl.JStartupClusterManagerImpl.getSapControl(JStartupClusterManagerImpl.java:223)
at com.sap.engine.services.dc.jstartup.impl.JStartupClusterManagerImpl.restartCluster(JStartupClusterManagerImpl.java:187)
... 19 more
Caused by: com.sap.engine.services.webservices.espbase.wsdl.exceptions.WSDLException: Content is not allowed in prolog.
at com.sap.engine.services.webservices.tools.SharedDocumentBuilders.loadDOMDocument(SharedDocumentBuilders.java:290)
at com.sap.engine.services.webservices.espbase.wsdl.WSDLLoader.load(WSDLLoader.java:100)
at com.sap.engine.services.webservices.espbase.wsdl.WSDLLoader.load(WSDLLoader.java:74)
at com.sap.engine.services.webservices.espbase.client.jaxws.core.SAPServiceDelegate.loadWSDLDefinitions(SAPServiceDelegate.java:220)
... 26 more
Caused by: org.xml.sax.SAXParseException: Content is not allowed in prolog.
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:247)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:284)
at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:199)
at com.sap.engine.services.webservices.tools.SharedDocumentBuilders.parse(SharedDocumentBuilders.java:180)
at com.sap.engine.services.webservices.tools.SharedDocumentBuilders.loadDOMDocument(SharedDocumentBuilders.java:276)
... 29 more

The issue can happen in the Application Server (AS) Java itself, or in the Shadow Instance of the AS Java created by the SUM.

The failure may happen in preprocessing or processing phase of the SUM upgrade.

SAP NetWeaver Application Server Java

An error occurred while restarting the server, Content is not allowed in prolog, SUM, upgrade, update, shadow, instance, sapcontrol, sapstartsrv, kernel, application server, java, as, netweaver, core, webservice, webservices, web, service, server , KBA , BC-JAS-SF , Startup Framework , Problem