Dspace 6.3 server is stoping after some times, and needs to restart the tomcat every 4-5 hours.

[prav...@gmail.com]

The below are the system generated email from the dspace server and its too many emails generated by system.

Using Dspace : 6.3

Tomcat : 8.5.12

Ubuntu :16.04

Content-Transfer-Encoding: 7bit
An internal server error occurred on http://localhost:8080/xmlui:

Date:       25/7/25 7:41 PM
Session ID: 9FB8832952BA3F7FDE602163EE7EB2B8

User:       Anonymous

IP address: 127.0.0.1

-- URL Was: http://dspace.localhist.com/jspui/browse?type=author&value=ILLE+B.
-- Method: GET
-- Parameters were:
-- type: "author"
-- value: "ILLE B."


Exception:
javax.servlet.ServletException: Servlet execution threw an exception
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
        at org.dspace.utils.servlet.DSpaceWebappServletFilter.doFilter(DSpaceWebappServletFilter.java:78)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
        at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:341)
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1441)
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NoClassDefFoundError: Could not initialize class org.dspace.sort.OrderFormat
        at org.dspace.browse.BrowseEngine.browseByItem(BrowseEngine.java:223)
        at org.dspace.browse.BrowseEngine.browse(BrowseEngine.java:102)
        at org.dspace.app.webui.servlet.AbstractBrowserServlet.processBrowse(AbstractBrowserServlet.java:338)
        at org.dspace.app.webui.servlet.BrowserServlet.doDSGet(BrowserServlet.java:89)
        at org.dspace.app.webui.servlet.DSpaceServlet.processRequest(DSpaceServlet.java:126)
        at org.dspace.app.webui.servlet.DSpaceServlet.doGet(DSpaceServlet.java:73)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
        ... 24 more

*** HEADER EXTRACTED active/CC430509F0FE ***

*** MESSAGE FILE END active/CC430509F0FE ***

Thanks in advance for any guidance.