我先解释一下我要干什么：这里要实现学生登录的功能，如果不是第一次登录的话，就判断输入的密码是否正确即可。如果是第一次进入系统点击登录的话，输入学号，并把第一次输入的密码作为以后登录的密码，然后把学号和密码插入到学生库中。以下是我的代码：
protected void Login_Authenticate(object sender, AuthenticateEventArgs e)
    {
        bool Authenticated = false;
        Authenticated = AuthenticationMethod(Login.UserName, Login.Password);
        e.Authenticated = Authenticated;
        if (Authenticated == true)
        {
            Response.Redirect("Default.aspx");
        }
    }
    private bool AuthenticationMethod(string UserName,string Password)
    {
        bool boolReturnValue = false;
        string connstr = "server=(local);Initial Catalog=test;Integrated Security=SSPI";
        SqlConnection conn=new SqlConnection(connstr);
        conn.Open();
        string sqlstr = "select * from student";
        SqlCommand cmd = new SqlCommand(sqlstr,conn);
        SqlDataReader Dr;
        Dr = cmd.ExecuteReader();
        while (Dr.Read())
        {
            if (UserName == Dr["sid"].ToString())        //该学号已存在，判断输入密码是否正确
            {
                if (Password == Dr["spwd"].ToString())
                {
                    boolReturnValue = true;
                }
                Dr.Close();
                return boolReturnValue;
            }
            else                             不存在学号的话说明是第一次登录，把学号密码存库
            {
                string inSql = "Insert student(sid,spwd) values ('" + UserName + "','" + Password + "')";
                SqlCommand command = new SqlCommand(inSql,conn);
                command.ExecuteNonQuery();
                conn.Close();
                boolReturnValue = true;
                return boolReturnValue;
            }
        }
        return boolReturnValue;
    }
    红色部分的代码这是其中一个版本，但是我改过的版本都不正确，老是报错，类似下面的错误
已有打开的与此 Command 相关联的 DataReader，必须首先将它关闭。
请给位高手指点帮助解决一下，非常感谢。

不解！

private bool AuthenticationMethod(string UserName,string Password)
    {
        bool bFlag = false;
        bool boolReturnValue = false;
        string connstr = "server=(local);Initial Catalog=test;Integrated Security=SSPI";
        SqlConnection conn=new SqlConnection(connstr);
        conn.Open();
        string sqlstr = "select * from student";
        SqlCommand cmd = new SqlCommand(sqlstr,conn);
        SqlDataReader Dr;
        Dr = cmd.ExecuteReader();
        while (Dr.Read())
        {
            if (UserName == Dr["sid"].ToString())        //该学号已存在，判断输入密码是否正确
            {
                if (Password == Dr["spwd"].ToString())
                {
                    boolReturnValue = true;
                    bFlag = true;
                }
              }
        }
        Dr.Close();

            //不存在学号的话说明是第一次登录，把学号密码存库
            if(false == bFlag)
            {
                string inSql = "Insert student(sid,spwd) values ('" + UserName + "','" + Password + "')";
                SqlCommand command = new SqlCommand(inSql,conn);
                command.ExecuteNonQuery();
                conn.Close();
                boolReturnValue = true;
            }

            return boolReturnValue;
    }

哇  这样子问题就解决了   谢谢

3L真有耐心！

很好的一个例子，学习了呵呵……