把JBPM部署到tomcat6下的时候报出如下异常： 
java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/index_jsp, and the class loader (instance of org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different Class objects for the type javax/el/ExpressionFactory used in the signature  org.apache.jsp.index_jsp._jspInit(index_jsp.java:23)  org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)  org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:159)  org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:329)  org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)  org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)  javax.servlet.http.HttpServlet.service(HttpServlet.java:717)  org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88)  org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)  org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)   
原因是项目中WEB-INF\lib中的三个jar包(juel.jar, juel-engine.jar, juel-impl.jar)和
tomcat6下lib中jar包(el-api.jar)冲突
解决方法：
方法一：换成tomcat5.5 一点问题也没有了
方法二：将juel.jar, juel-engine.jar, juel-impl.jar这三个包复制到tomcat6下lib中，
并删除原来的el-api.jar，切记要把WEB-INF\lib中的juel.jar, juel-engine.jar, juel-impl.jar删除。
不然还是要冲突。