excel检测到xls 是sylk文件 解决

在做excel导入时候出现如上图情况，原因是：

SYLK 文件时一个文本文件，开头的为“ID”或“ID_XXXX”（其中XXXX是文本字符串）。
SYLK 文件的第一个的记录是在 ID_Number 记录的。
Excel 将识别该文本在文本文件开头时, 它会将该文件解释为 SYLK 文件。
Excel 将尝试从该 SYLK 格式转换该文件，但不能这样做，因为"ID"字符后不有任何有效的 SYLK 代码。 
因为 Excel 不能转换该文件，您收到错误消息。

例子如下：

  public void Import()
    {
        DataTable dt = GetData();
        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename="+DateTime.Now.ToString("yyyyMMddhhmmssfff")+".xls");
        Response.ContentEncoding = Encoding.GetEncoding("gb2312");
        Response.ContentType = "application/ms-excel";
        StringWriter sw = new StringWriter();
        ArrayList list = new ArrayList();
        string connstr = "";
        for (int i = 0; i < dt.Columns.Count; i++)
        {
            connstr = connstr + dt.Columns[i].ColumnName + "\t";
            list.Add(dt.Columns[i].ColumnName);
        }
        connstr = connstr.Substring(0, connstr.Length - 1);
        sw.WriteLine(connstr);
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            connstr = "";
            for (int j = 0; j < dt.Columns.Count; j++)
            {
                connstr = connstr + dt.Rows[i][list[j].ToString()].ToString() + "\t";
            }
            connstr = connstr.Substring(0, connstr.Length - 1);
            sw.WriteLine(connstr);
        }
        Response.Write(sw.ToString());
        Response.Flush();
        Response.Close();
    }
    public DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("ID_Numeric", typeof(string));
        dt.Columns.Add("productname", typeof(string));
        DataRow dr = dt.NewRow();
        dr["ID_Numeric"] = "1";
        dr["productname"]="氯化钠注射液";
        dt.Rows.Add(dr);
        dr = dt.NewRow();
        dr["ID_Numeric"] = "2";
        dr["productname"] = "氯化钾注射液";
        dt.Rows.Add(dr);
        return dt;
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Import();
    }

将ID或者ID_Numeric转换成小写字母就可以解决问题：

例子如下：

    public void Import()
    {
        DataTable dt = GetData();
        Response.Clear();
        Response.AddHeader("content-disposition", "attachment;filename="+DateTime.Now.ToString("yyyyMMddhhmmssfff")+".xls");
        Response.ContentEncoding = Encoding.GetEncoding("gb2312");
        Response.ContentType = "application/ms-excel";
        StringWriter sw = new StringWriter();
        ArrayList list = new ArrayList();
        string connstr = "";
        for (int i = 0; i < dt.Columns.Count; i++)
        {
            connstr = connstr + dt.Columns[i].ColumnName + "\t";
            list.Add(dt.Columns[i].ColumnName);
        }
        connstr = connstr.Substring(0, connstr.Length - 1);
        sw.WriteLine(connstr);
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            connstr = "";
            for (int j = 0; j < dt.Columns.Count; j++)
            {
                connstr = connstr + dt.Rows[i][list[j].ToString()].ToString() + "\t";
            }
            connstr = connstr.Substring(0, connstr.Length - 1);
            sw.WriteLine(connstr);
        }
        Response.Write(sw.ToString());
        Response.Flush();
        Response.Close();
    }
    public DataTable GetData()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("Id_Numeric", typeof(string));
        dt.Columns.Add("productname", typeof(string));
        DataRow dr = dt.NewRow();
        dr["Id_Numeric"] = "1";
        dr["productname"]="氯化钠注射液";
        dt.Rows.Add(dr);
        dr = dt.NewRow();
        dr["Id_Numeric"] = "2";
        dr["productname"] = "氯化钾注射液";
        dt.Rows.Add(dr);
        return dt;
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        Import();
    }