Error compiling GWT - eclipse

Question

After doing some changes to my GWT project (adding protected-resources)I can no longer launch it.
It gives a 500 while trying to use the GWT developer plugin. Once I had a similar error (Invalid pc in LineNumberTable in class) in another project which I solved setting GWT 2.x as the top library in the build path order of my Eclipse 3.6 IDE.
20-feb-2012 19:00:33 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.ClassFormatError: Invalid pc in LineNumberTable in class file org/eclipse/jdt/internal/compiler/lookup/TypeBinding
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.eclipse.jdt.internal.compiler.Compiler.<init>(Compiler.java:260)
at org.eclipse.jdt.internal.compiler.Compiler.<init>(Compiler.java:153)
at org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:423)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:349)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:327)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:314)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:589)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:317)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:558)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:859)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:579)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1555)
at java.lang.Thread.run(Thread.java:662)
Edit: classpath
<classpath>
<classpathentry exported="true" kind="con" path="com.google.gwt.eclipse.core.GWT_CONTAINER/GWT"/>
<classpathentry kind="src" path="src"/>
<classpathentry kind="src" output="test-classes" path="test"/>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
<classpathentry kind="con" path="org.eclipse.jst.server.core.container/org.eclipse.jst.server.tomcat.runtimeTarget/Apache Tomcat v6.0"/>
<classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
<classpathentry kind="lib" path="C:/eclipse/plugins/com.google.gwt.eclipse.sdkbundle_2.4.0.v201201120043-rel-r36/gwt-2.4.0/validation-api-1.0.0.GA-sources.jar"/>
<classpathentry kind="lib" path="C:/eclipse/plugins/com.google.gwt.eclipse.sdkbundle_2.4.0.v201201120043-rel-r36/gwt-2.4.0/validation-api-1.0.0.GA.jar" sourcepath="C:/eclipse/plugins/com.google.gwt.eclipse.sdkbundle_2.4.0.v201201120043-rel-r36/gwt-2.4.0/validation-api-1.0.0.GA-sources.jar"/>
<classpathentry kind="lib" path="WebContent/WEB-INF/lib/sqljdbc4.jar"/>
<classpathentry kind="lib" path="WebContent/WEB-INF/lib/NeptunoMetascada.jar"/>
<classpathentry kind="lib" path="WebContent/WEB-INF/lib/slf4j-api-1.6.4.jar"/>
<classpathentry kind="lib" path="WebContent/WEB-INF/lib/slf4j-jdk14-1.6.4.jar"/>
<classpathentry kind="output" path="WebContent/WEB-INF/classes"/>
</classpath>

Answer 1

I'm not exactly sure if this helps with your problem, but there are a couple of things that look suspect to me.
First, I'd remove the separate validation-api entries, as they're part of the GWT container anyway.
Second, the GWT container is marked as being exported, which should not be necessary. All you should need is the gwt-servlet.jar in your WEB-INF/lib, which doesn't need a separate classpath entry as it's in the web app libraries.
Third, it looks as if the web app libraries container is missing, where you have a couple of jars listed explicitly:
<classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.web.container"/>
As mentioned, I'm not too sure if this helps your actual problem - it just looked odd to me.