调试易

我写了一个登录窗口，在登录窗口上有修改密码的按钮，点击修改密码后会弹出修改密码的窗体；可修改密码后（数据库内数据已更新）登录窗口无法登录，一直报密码错误！请各位大侠帮忙
数据库名为db_canting  ，  用户信息保存在表emplyee中UserName  UserPass
登录窗体loginin
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;namespace canting
{
    public partial class Loginin : Form
    {        
        public Loginin()
        {
            InitializeComponent();  //初始化窗口
               }        private void login_Click(object sender, EventArgs e)  //登录按钮
        {
           
            string username = string.Empty , password = string.Empty ;
            string sqlconstr = "server=127.0.0.1; database=db_canting;uid=**;pwd=****";  //连接数据库db_canting
                SqlConnection dataConnection = new SqlConnection(sqlconstr);               
            try
            {
               
                dataConnection.Open();
            }
            catch (SqlException eaccessdb)    //捕捉数据库连接异常
                    {
                MessageBox.Show(eaccessdb.Message);
            }            SqlCommand sqlcomm = new SqlCommand("select * from tb_employee where UserName='" + usernametext.Text + "'");                         //检索用户名
                     sqlcomm.Connection = dataConnection;
        
            SqlDataReader reader = sqlcomm.ExecuteReader();
            if(reader.Read())
              {
                  username = reader.GetValue(8).ToString(); //获得用户名称
                               password = reader.GetValue(9).ToString(); //获得用户密码
                               reader.Close();
                  dataConnection.Close(); 
                    if(username==usernametext.Text)
                       {
                          
    
                        MessageBox.Show(password);
                         MessageBox.Show(passwordtext.Text);
                      
                            if (passwordtext.Text==password)       //如果用户名与密码匹配
                                                       {
                                   MessageBox.Show("登录成功");     //载入主窗体
                                                        }
                           else
                                { 
                                   MessageBox.Show("密码错误！！！","提      示",MessageBoxButtons.OK,MessageBoxIcon.Warning);
                                   passwordtext.Text=String.Empty; //如果密码错误则提示密码错误
                                                            }
              
                         }
              }
            else
              {
                MessageBox.Show("用户名错误！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                usernametext.Text = String.Empty;         //如果用户名错误则提示用户名错误
                            passwordtext.Text = String.Empty;         //如果密码错误则提示密码错误
                          }
            dataConnection.Close();            //关闭数据库连接        }      
        
        
        
        private void changepassword_Click(object sender, EventArgs e)
        {
            changepassword chapa = new changepassword();//调用用户修改密码窗体
                     chapa.ShowDialog();
        }
                   private void canclelogin_Click(object sender, EventArgs e)
        {
            this.Close();
        }
        
    }
}
修改密码窗体   changepassword
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;namespace canting
{
    public partial class changepassword : Form
    {
        public changepassword()
        {
            InitializeComponent();
        }        private void changepassword_Load(object sender, EventArgs e)
        {        }        private void makesurechange_Click(object sender, EventArgs e)
        {            if (usernameforchange.Text == "" || oldpassword.Text == ""||newpassword.Text==""||newpasswordagain.Text=="")
            {
                MessageBox.Show("请将登录名、密码填写完整！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
            }
            else
            {
                string usernamechange = string.Empty, passwordchange = string.Empty;
                string sqlconstrchange = "server=127.0.0.1; database=db_canting;uid=sa;pwd=802331";  //连接数据库db_canting
                SqlConnection dataConnectionchange = new SqlConnection(sqlconstrchange);
                try
                {                    dataConnectionchange.Open();
                }
                catch (SqlException eaccessdb)    //捕捉数据库连接异常
                {
                    MessageBox.Show(eaccessdb.Message);
                }                SqlCommand sqlcommchange = new SqlCommand("select * from tb_employee where UserName= '" + usernameforchange.Text + "'");  //检索用户名
                sqlcommchange.Connection = dataConnectionchange;                SqlDataReader readerchange = sqlcommchange.ExecuteReader();
                if (readerchange.Read())
                {                    usernamechange = readerchange.GetValue(8).ToString(); //获得用户名称
                    passwordchange = readerchange.GetValue(9).ToString(); //获得用户密码                    if (usernamechange == usernameforchange.Text)
                    {                        if (passwordchange == oldpassword.Text)
                        {
                            if (newpassword.Text != newpasswordagain.Text)
                            {
                                MessageBox.Show("新两次输入不一致", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);                            }
                            else
                            {
                                readerchange.Close();
                                SqlDataAdapter sqlda = new SqlDataAdapter("select * from tb_emplyee", dataConnectionchange);
                                SqlCommand sqlcomm2 = new SqlCommand("update tb_employee set UserPass='" + newpassword.Text + " ' where UserName='" + usernameforchange.Text + "'");
                                sqlcomm2.Connection = dataConnectionchange;
                               sqlda.UpdateCommand = sqlcomm2;
                              sqlda.UpdateCommand.ExecuteNonQuery();
                            
                                MessageBox.Show("修改成功");
                                dataConnectionchange.Close();
                        
                                this.Close();
                            }                        }
                        else
                        {
                            MessageBox.Show("用户名或密码错误！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                        }
                    }                }
                else
                {
                    MessageBox.Show("不存在该用户名！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Warning);
                }
                dataConnectionchange.Close();
            }
           
            
        }        private void cancelchange_Click(object sender, EventArgs e)
        {
            this.Close();
        }
   
       
    }
}