The Spotfire Server could become inaccessible and the following error can be seen in the browser while accessing the Server URL.
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TYPE Exception Report

MESSAGE java.lang.NoSuchMethodError: java.el.ExpressionFcttory.newInstance()Ljavax/el/ExpressionFactory;

Description The Server encountered an unexpected condition that prevented in from fulfilling the request.
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Screenshot(error.jpg) is attached for reference.

Catalina.log will show a similar error as follows.
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SEVERE [http-nio-80-exec-7] org.apache.catalina.core.StandardHostValve.custom Exception Processing ErrorPage[errorCode=0, location=/error.jsp]
 javax.servlet.ServletException: java.lang.NoSuchMethodError: javax.el.ExpressionFactory.newInstance()Ljavax/el/ExpressionFactory;
    at org.apache.jsp.error_jsp._jspService(error_jsp.java:128)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728)
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:472)
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:395)
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:316)
    at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:395)
    at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:254)
    at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:349)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:175)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
    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.NoSuchMethodError: javax.el.ExpressionFactory.newInstance()Ljavax/el/ExpressionFactory;
    at org.apache.jasper.runtime.JspApplicationContextImpl.<init>(JspApplicationContextImpl.java:48)
    at org.apache.jasper.runtime.JspApplicationContextImpl.getInstance(JspApplicationContextImpl.java:77)
    at org.apache.jasper.runtime.PageContextImpl.initialize(PageContextImpl.java:133)
    at org.apache.jasper.runtime.JspFactoryImpl.internalGetPageContext(JspFactoryImpl.java:109)
    at org.apache.jasper.runtime.JspFactoryImpl.getPageContext(JspFactoryImpl.java:60)
    at org.apache.jsp.error_jsp._jspService(error_jsp.java:97)
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Spotfire Server not accessible

All supported environments

This error can come up for the following reasons:
#1) If any of the required jar files missing in the "Installation Directory\tibco\tss\version\tomcat\lib"
OR
#2) If an incompatible jar file has been placed under "Installation Directory\tibco\tss\version\tomcat\lib"

To address this issue, make sure to replace any jar file that was removed before the server stopped working or remove any additional jar file that has been added recently.

** Another workaround would be to copy the "lib" folder under "Installation Directory\tibco\tss\version\tomcat\" from a working environment  (of the same version and the hotfix level as the non-working environment) and paste the same under  "Installation Directory\tibco\tss\version\tomcat" of the non working environment.

Note: Take a backup of the "tomcat\lib" folder in the non working environment before making any changes.