Invalid column name 'Jan'.Same for All months

using System;

using System.Data;

using System.Configuration;

using System.Collections;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Web.UI.HtmlControls;

using System.Data.SqlClient;

public partial class Er_TimeSheetHistory : System.Web.UI.Page

public string strcon1 = "Data Source=LENOVO-EF645A82;AttachDbFilename=E:\\ERSYSTEMS_WEB_1\\DataSourse\\EmpDb1.mdf;Initial Catalog=Erdata;Integrated Security=True";

public string WelcomeName;

SqlDataReader dr;

SqlParameter mparam, yparam;

SqlCommand cmd;

protected void Page_Load(object sender, EventArgs e)

WelcomeName = Session["userid"].ToString();

//lbldate.Text = DateTime.Now.ToString ();

DateTime Date = DateTime.Now;

Label2.Text = Date.ToString("MMMM");

Label3.Text = Date.ToString("yyyy");

BtnSubmit.Enabled = false;

protected void BtnSubmit_Click1(object sender, EventArgs e)

HtmlForm frm=new HtmlForm() ;

Response.AddHeader("content-disposition", "attachment;filename=FileName.xls");

Response.Charset = "";

Response.Cache.SetCacheability(HttpCacheability.NoCache);

Response.ContentType = "application/vnd.xls";

System.IO.StringWriter stringWrite = new System.IO.StringWriter();

System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);

//frm.Attributes.Add("runat", "server");

//GridView1.Attributes.Add("runat", "server");

//GridView1.RenderControl(htmlWrite);

protected void Button1_Click(object sender, EventArgs e)

public void Bindgrid()

SqlConnection conn = new SqlConnection(strcon1);

SqlDataAdapter da = new SqlDataAdapter("select * from D_TimeSheet1 where EmpId=" + Session["usid"] + " AND Year=" +lstyear .SelectedValue + " AND Months="+DropDownList1 .SelectedValue.ToString () +" order By AttDate DESC", conn);

DataSet ds = new DataSet();

da.Fill(ds, "D_TimeSheet1");

// Filling a employee table

DataTable dt = ds.Tables["D_TimeSheet1"];

dt = RemoveDuplicateRows(dt, "EmpId");

DataGrid1.DataSource = ds.Tables["D_TimeSheet1"].DefaultView;

public DataTable RemoveDuplicateRows(DataTable dTable, string AttDate)

Hashtable hTable = new Hashtable();

ArrayList duplicateList = new ArrayList();

//Add list of all the unique item value to hashtable, which stores combination of key, value pair.

//And add duplicate item value in arraylist.

foreach (DataRow drow in dTable.Rows)

if (hTable.Contains(drow[AttDate]))

else

hTable.Add(drow[AttDate], string.Empty);

//Removing a list of duplicate items from datatable.

foreach (DataRow dRow in duplicateList)

//Datatable which contains unique records will be return as output.

return dTable;