通过C向SQL表中插入值时出现异常#

嗨,我让manullay创建了textbox,然后用它创建了一个新用户。我使用SQL SERVER 2005作为后端,Visual SERVER 2008作为前端。。

我有这个LoginAccount表,它存储了新用户创建的详细信息。当我单击按钮时(在该按钮中我编写了通过SQLInsert创建新用户的代码),

  string strConnection = ConfigurationManager.ConnectionStrings"FHDLConnectionString"].ToString();
        SqlConnection sqlConnection = new SqlConnection(strConnection);
        string username = TextBox1.Text;
        string password = TextBox2.Text;
        string confirmpass = TextBox3.Text;
        string SQLQuery = "Select username From LoginAccount where '" + username + "'";
        string SQLQuery1 = "Insert into LoginAccount values ('" + username + "','" + password + "')";

        SqlCommand command = new SqlCommand(SQLQuery, sqlConnection);
        SqlCommand command1 = new SqlCommand(SQLQuery1, sqlConnection);

        sqlConnection.Open();
        string CheckUsername = "";

        if (password.ToString() != confirmpass.ToString())
        {
            Literal1.Text = " Password's does not match ";
        }
        else
        {
            try
            {
                CheckUsername = command.ExecuteScalar().ToString();
            }
            catch (Exception er)
            {
                Literal1.Text = " Username already exists ";
            }

            string insertQuery = "";

            try
            {
                insertQuery = command1.ExecuteScalar().ToString();
                Server.Transfer("Login_Created.aspx");
            }
            catch (Exception er)
            {
                Literal1.Text = " Could not create the user, Please retry with some other option ";
            }
        }
        sqlConnection.Close();

在“fhdl”附近预期条件的上下文中指定的非布尔型表达式

和

这是最后一次接球。

但最主要的是我能够插入用户名和密码到loginacount表!!!!!!! i、 当我看到表内容时,我可以看到在该表中创建的新用户。 另一件事是 此代码以前完美执行过一次,但现在没有:( 谁能告诉我哪里出了问题吗?