I have tried Googling, looking at message boards, posting on message boards,
etc. and no one seems to know anything about this problem. I'm running Apache
Web Server 2.0.54 connected to Tomcat 5.5.9 by the mod_jk2 connector. 

When I try to access a JSP, I get the error:

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: Provider
org.apache.xerces.jaxp.SAXParserFactoryImpl could not be instantiated:
java.lang.NullPointerException
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:249)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

root cause

javax.xml.parsers.FactoryConfigurationError: Provider
org.apache.xerces.jaxp.SAXParserFactoryImpl could not be instantiated:
java.lang.NullPointerException
javax.xml.parsers.SAXParserFactory.newInstance(Unknown Source)
org.apache.taglibs.standard.tlv.JstlBaseTLV.validate(Unknown Source)
org.apache.jasper.compiler.TagLibraryInfoImpl.validate(TagLibraryInfoImpl.java: 750)
org.apache.jasper.compiler.Validator.validateXmlView(Validator.java:1527)
org.apache.jasper.compiler.Validator.validate(Validator.java:1495)
org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:157)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:286)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:267)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:255)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:556)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:293)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

note The full stack trace of the root cause is available in the Apache
Tomcat/5.5.9 logs.
Apache Tomcat/5.5.9

Stopping and restarting the Tomcat service consistently seems to fix the
problem. To say I can consistenty reproduce the error is probably not accurate,
but it seems to manifest itself every time I significantly modify a JSP. (i.e.
When I modify a JSP, I get the error and have to restart Tomcat.)

The following shows up in the localhost.2005.06.06.log file:

Jun 6, 2005 8:51:43 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
javax.xml.parsers.FactoryConfigurationError: Provider
org.apache.xerces.jaxp.SAXParserFactoryImpl could not be instantiated:
java.lang.NullPointerException
	at javax.xml.parsers.SAXParserFactory.newInstance(Unknown Source)
	at org.apache.taglibs.standard.tlv.JstlBaseTLV.validate(JstlBaseTLV.java:152)
	at org.apache.taglibs.standard.tlv.JstlCoreTLV.validate(JstlCoreTLV.java:96)
	at
org.apache.jasper.compiler.TagLibraryInfoImpl.validate(TagLibraryInfoImpl.java:750)
	at org.apache.jasper.compiler.Validator.validateXmlView(Validator.java:1527)
	at org.apache.jasper.compiler.Validator.validate(Validator.java:1495)
	at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:157)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:286)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:267)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:255)
	at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:556)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:293)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
	at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
	at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
	at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
	at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
	at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
	at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:307)
	at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:385)
	at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:748)
	at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:678)
	at org.apache.jk.common.SocketConnection.runIt(ChannelSocket.java:871)
	at
org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
	at java.lang.Thread.run(Unknown Source)

The web.xml file for the application is as follows:

<?xml version="1.0" encoding="ISO-8859-1"?>
 
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
    version="2.4">
 
	<display-name>Madisonville Community College Online Workshop Quiz Grading
Tools</display-name>
	<description>
		Servlets and JSPs for evaluating the results of online quizzes at the end of
online workshops.
	</description>
 
	<servlet>
		<servlet-name>QuizGrader</servlet-name>
		<servlet-class>QuizGraderServlet</servlet-class>
	</servlet>
 
	<servlet-mapping>
		<servlet-name>QuizGrader</servlet-name>
		<url-pattern>/quizgrader</url-pattern>
	</servlet-mapping>
 
</web-app>

I've posted this on the Java Developer forum twice and on HTMLforums.com once
and have received no replies.