upload file and some field items to document library

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SharePoint

To upload a document to sharepoint document library i did like this :

string strsite = "sharepoint site";
using (SPSite mySite = new SPSite(strsite))
{
using (SPWeb web = mySite.OpenWeb())
{
SPFolder folder = web.Folders["QEHS Manual"];
SPFileCollection filecol = folder.Files;
Boolean replaceExistingFiles = true;
string filename = System.IO.Path.GetFileName(FileUpload1.PostedFile.FileName);
byte[] contents = new byte[Convert.ToInt32(FileUpload1.PostedFile.ContentLength)];
SPFile addedFile = filecol.Add(filename, contents, replaceExistingFiles);
SPItem newItem = addedFile.Item;
newItem["No."] = txtno.Text;
newItem["Document Description"] = txtdocdescription.Text;
newItem["Document No."] = txtdocno.Text;
newItem["Custodian"] = txtcustodian.Text;
newItem["Revision No."] = txtrevno.Text;
newItem["Issue No."] = txtissueno.Text;
newItem.Update();
addedFile.Update();
}
}

the file gets uploaded. but when iam trying to pen it from sharepoint site, it is showning error.the error message is """the office open xml file xxx cannot be opened because there are problems with content""" can anyone pls help me..