error in excel uploading

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C#5.0

MVC5

I am uploading a excel file when the uploaded excel file is not proper format ist giveing error but after that also when i am inserting a proper excel file its given same error also

when uploading 1st time proper excel format working fine then wrong excel format error againg going for proper format also its giving error

try
{
    string fileExtension =
                         System.IO.Path.GetExtension(Request.Files["file"].FileName);

    if (fileExtension == ".xls" || fileExtension == ".xlsx")
    {
        string fileLocation = Server.MapPath("~/ExcelUpload/") + Request.Files["file"].FileName;
        if (System.IO.File.Exists(fileLocation))
        {

            System.IO.File.Delete(fileLocation);
        }
        Request.Files["file"].SaveAs(fileLocation);
        string excelConnectionString = string.Empty;
        excelConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" +
        fileLocation + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=2\"";
        //connection String for xls file format.
        if (fileExtension == ".xls")
        {
            excelConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" +
            fileLocation + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=2\"";
        }
        //connection String for xlsx file format.
        else if (fileExtension == ".xlsx")
        {
            excelConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" +
            fileLocation + ";Extended Properties=\"Excel 12.0;HDR=Yes;IMEX=2\"";
        }
        //Create Connection to Excel work book and add oledb namespace
        OleDbConnection excelConnection = new OleDbConnection(excelConnectionString);
        excelConnection.Open();
        DataTable dt = new DataTable();

        dt = excelConnection.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
        if (dt == null)
        {
            return null;
        }

        String[] excelSheets = new String[dt.Rows.Count];
        int t = 0;
        //excel data saves in temp file here.
        foreach (DataRow row in dt.Rows)
        {
            excelSheets[t] = row["TABLE_NAME"].ToString();
            t++;
        }
        OleDbConnection excelConnection1 = new OleDbConnection(excelConnectionString);


        string query = string.Format("Select * from [{0}]", excelSheets[0]);
        using (OleDbDataAdapter dataAdapter = new OleDbDataAdapter(query, excelConnection1))
        {
            dataAdapter.Fill(ds);
        }
    }
    //if (fileExtension.ToString().ToLower().Equals(".xml"))
    //{
    //    string fileLocation = Server.MapPath("~/ExcelUpload/") + Request.Files["FileUpload"].FileName;
    //    if (System.IO.File.Exists(fileLocation))
    //    {
    //        System.IO.File.Delete(fileLocation);
    //    }

    //    Request.Files["FileUpload"].SaveAs(fileLocation);
    //    XmlTextReader xmlreader = new XmlTextReader(fileLocation);

    //    ds.ReadXml(xmlreader);
    //    xmlreader.Close();
    //}
    //  Allquestions alqnn = new Allquestions();



    for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
    {
        //string conn = ConfigurationManager.ConnectionStrings["dbconnection"].ConnectionString;
        SqlConnection con = new SqlConnection(conn);
        string query = "Insert into ALQuestion.QuestionMaster(Question,Option1,Option2,Option3,Option4,Answer,LevelID,SkillID,CreatedOn,Status) Values('" +
        ds.Tables[0].Rows[i][00].ToString() + "','" + ds.Tables[0].Rows[i][01].ToString() +
        "','" + ds.Tables[0].Rows[i][02].ToString() + "','" + ds.Tables[0].Rows[i][03].ToString() + "','" + ds.Tables[0].Rows[i][04].ToString() + "','" + ds.Tables[0].Rows[i][05].ToString() + "','" + LevelId.ToString() + "','" + skillid.ToString() + "','" + now.ToString(("yyyy/MM/dd")) + "','" + "1" + "')";

        con.Open();
        SqlCommand cmd = new SqlCommand(query, con);
        cmd.ExecuteNonQuery();
        con.Close();

    }


    ViewBag.UploadExcelStatus = "Excel Upload Successfully";
    return Json("Excel Upload Successfully");
}
catch
{

    ViewBag.UploadExcelStatus = "Please Upload a Proper Excel File";

    return Json(Please Upload a Proper Excel File");
}


its coming directly to catch