我用JBuilder2006加载Servlet时，出错了java.lang.ClassNotFoundException: myservlet.UserallServlet，请问，各位大虾，这个时什么原因

以下是我的jsp页面和web.xml
index.jsp
<%@ page contentType="text/html; charset=GB18030" import="myservlet.*"%>
<html>
<head>
<title>
index
</title>
</head>
<body bgcolor="#ffffff">
<form method=post action="userallservlet">
<br><br>
<input type="submit" name="Submit" value="查询会员信息">
<input type="reset" value="Reset">
</form>
</body>
</html>
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<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>Web</display-name>
  <servlet>
    <servlet-name>userallservlet</servlet-name>
    <servlet-class>myservlet.UserallServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>userallservlet</servlet-name>
    <url-pattern>/userallservlet</url-pattern>
  </servlet-mapping>
  <servlet>
    <description>Added by JBuilder to compile JSPs with debug info</description>
    <servlet-name>debugjsp</servlet-name>
    <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
    <init-param>
      <param-name>classdebuginfo</param-name>
      <param-value>true</param-value>
    </init-param>
    <load-on-startup>3</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>debugjsp</servlet-name>
    <url-pattern>*.jsp</url-pattern>
  </servlet-mapping>
</web-app>
在这里先谢谢了