[Access]出现BUG了

请看代码 这是在asp.net 的 C# 代码 目的是为了验证 数据库是否存在已经有的用户名
但我在数据库中录入一条记录后 在网页中验证 还是显示“用户名未被使用”protected void TextBox_Username_TextChanged(object sender, EventArgs e)
    {
        try
        {
            TextBox_Username.Text = TextBox_Username.Text.Trim();
            Label_SameUsername.Visible = true;
            if (TextBox_Username.Text != "")
            {
                String Sqlstr = null;
                Sqlstr = "SELECT DISTINCT * FROM Account WHERE ACalled=" +
                    "'" + TextBox_Username.Text + "'" +
                    ";";
                /*Sqlstr = "SELECT Aid FROM Account WHERE ACalled=" +
                    "'"+ TextBox_Username.Text + "'" +
                    ";";*/
                if (CheckSameValue(Sqlstr))
                {
                    Label_SameUsername.Text = "* 用户名已被使用";
                    Label_SameUsername.ForeColor = System.Drawing.Color.Red;
                }
                else
                {
                    Label_SameUsername.Text = "用户名可以使用";
                    Label_SameUsername.ForeColor = System.Drawing.Color.Green;
                }
            }
            else
            {
                Label_SameUsername.Text = "* 用户名不能为空";
                Label_SameUsername.ForeColor = System.Drawing.Color.Red;
            }
        }
        catch (System.Exception ex)
        {
            ErrorMSG.Visible = true;
            Label_ErrorMSG.Text = ex.Message;
        }
    }
    private bool CheckSameValue(String Sqlstr)
    {
        try
        {
            CntStr = ConfigurationManager.AppSettings["AccessDrv"] +
            HttpContext.Current.Server.MapPath("..\\") +
            ConfigurationManager.AppSettings["Database"];
            Cnt = new OleDbConnection(CntStr);
            Cnt.Open();
            Cmd = Cnt.CreateCommand();
            Cmd.CommandText = Sqlstr;
            if (Cmd.ExecuteNonQuery() >= 1)
            {
                return true;
            }
            else
            {
                return false;
            }
        }
        catch (Exception ex)
        {
            throw (ex);
        }
        finally
        {
            Cnt.Close();
        }
    }/******web.config*******/
<add key="AccessDrv" value="Provider=Microsoft.Jet.OleDb.4.0;Data Source="/>
    <add key="Database" value="App_Data\Database.mdb"/>
/******web.config*******/
我调试了一下看 似乎是 Cmd.ExecuteNonQuery() 这里返回0
但我用SQL执行 的确能查找到一条记录
坐等高手