C# - Getting Error When Open Word Document File Which Is Generated Using .net?

I am using below code to generate word document using assp.net/c#.net, please tell me where i am missing it is generating word file and all contents are their.but problem is that when i open it it gives me error:"The Office Open XML file filename.doc cannot be opened because there are problems with the contents"
and after clicking ok i get my required file.remove this error.

in error details:The file is corrupt and cannot be opened after it again gets a error message:"word found unreadable content in myfile.do you want to recover the contents of this document? if you trust the source of ths document,click yes"

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Office;

[code]...