用MyEclipse和TOMCAT 开发JSP文件时出现了这个错误，弄不明白

org.apache.jasper.JasperException: Unable to compile class for JSP

Generated servlet error:
D:\Program Files\Tomcat 5.0\work\Catalina\localhost\Myproject\org\apache\jsp\MyJsp_jsp.java:8: cannot access java.lang.Object


Generated servlet error:
bad class file: D:\Program Files\MyEclipse Enterprise Workbench 5.1.0 GA\jre\lib\rt.jar(java/lang/Object.class)
class file has wrong version 49.0, should be 48.0
Please remove or make sure it appears in the correct subdirectory of the classpath.
public final class MyJsp_jsp extends org.apache.jasper.runtime.HttpJspBase
             ^
1 error



    org.apache.(DefaultErrorHandler.java:84)
    org.apache.(ErrorDispatcher.java:332)
    org.apache.(Compiler.java:412)
    org.apache.(Compiler.java:472)
    org.apache.(Compiler.java:451)
    org.apache.(Compiler.java:439)
    org.apache.jasper.(JspCompilationContext.java:511)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
 请高手帮 我看看，问题出在哪里？
页面源代码没有问题！