我在Eclipse IDE中使用JSF 2.0。当我尝试实现JSP和Servlet时，出现以下错误：

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/exCrop_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
at org.apache.jsp.exCrop_jsp._jspInit(exCrop_jsp.java:31)
at org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:49)
at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:181)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:370)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:389)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

这是怎么引起的，我该如何解决？