ASP coding for website error

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;

public partial class Index : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(IsPostBack)
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["MemberInfoConnectionString"].ConnectionString);
            conn.Open();
            string checkuser = "select count(*) from SystemMemberInfo where Username="+ TextBoxUserName.Text +"'";
            SqlCommand com = new SqlCommand(checkuser, conn);
            int temp = Convert.ToInt32(com.ExecuteScalar().ToString());
            if (temp == 1)
            {
                Response.Write("User already Exists");
            }

            conn.Close();

        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["MemberInfoConnectionString"].ConnectionString);
            conn.Open();
            string insertQuery = "insert into SystemMemberInfo (Username,Email,Password,Minecraft Username) values (@Uname ,@email ,@password ,@mcuname)";
            SqlCommand com = new SqlCommand(insertQuery, conn);
            com.Parameters.AddWithValue("@Uname", TextBoxUserName.Text);
            com.Parameters.AddWithValue("@email", TextBoxEmail.Text);
            com.Parameters.AddWithValue("@password", TextBoxPassword.Text);
            com.Parameters.AddWithValue("@mcuname", TextBoxMcUserName.Text);

            com.ExecuteNonQuery();
            Response.Redirect("WebsiteSystem.aspx");
            Response.Write("Registration is successful.You can login now." );


            conn.Close();
        }
        catch(Exception ex)
        {
            Response.Write("Error:"+ex.ToString());
        }
    }
}