HTTP Status 500 - 

type Exception report

message 

description The server encountered an internal error () that prevented it from fulfilling this request.

exception 
javax.servlet.ServletException: Error allocating a servlet instance
	at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:617)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:164)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:139)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2460)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:133)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:119)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:127)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:157)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
	at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
	at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
	at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
	at java.lang.Thread.run(Unknown Source)

root cause 
java.lang.UnsupportedClassVersionError: Bad version number in .class file
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1787)
	at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:1049)
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1507)
	at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1386)
	at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:830)
	at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:613)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:164)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:139)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2460)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:133)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:119)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:594)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:127)
	at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:596)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:433)
	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:955)
	at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:157)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
	at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
	at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
	at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
	at java.lang.Thread.run(Unknown Source)