The type or namespace name 'DataBaseHelper' could not be found (are you missing a using directive or an assembly reference?)

protected void BindDataList()
    {
       string sqlCmd = "SELECT clogo FROM tbl_company";
        DataBaseHelper DBHelper = new DataBaseHelper();//error
        DataTable dt = DBHelper.GetTable(sqlCmd);//error
        //adding new column to display image
        DataColumn imageCol = new DataColumn("clogo", typeof(string));
        dt.Columns.Add(imageCol);
        
        if (dt.Rows.Count > 0)
        {
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                dt.Rows[i][imageCol] = string.Format
        ("<img src='Handler.ashx?id={0}' alt='' style='width:100px' />", 
            dt.Rows[i][0].ToString());
            }
        }