Error : The file has been modified by SHAREPOINT/system

I am creating .docx file using template of SharePoint Library and uploading it to the library. But I am facing an error while CheckOut(). Below is my code.

public void UpdateAndCreateFile(SPWeb web)
{
    try
    {
        SPSecurity.RunWithElevatedPrivileges(delegate()
        {
            string TemplateUrl = string.Empty;
            try
            {
                TemplateUrl = "template path";
            }
            catch { }


            web.AllowUnsafeUpdates = true;
            SPList olist = web.Lists["Document Library"];
            String url = olist.RootFolder.ServerRelativeUrl.ToString();


            string foldername = Convert.ToString("Foldername in document library");
            SPFolder newfolder = web.GetFolder(url + "/" + foldername);

            if (!newfolder.Exists)
            {
                SPFolderCollection folders = web.GetFolder(url).SubFolders;
                //Create new folder
                folders.Add(foldername);
            }

            SPFile file = null;

            file = web.GetFile("Your Document templated full path");

            if (file != null)
            {
                web.AllowUnsafeUpdates = true;
                Stream readStream = file.OpenBinaryStream(); //file is SPFile type
                SPFile uploadedFile = newfolder.Files.Add(newfolder.Url + @"/" + "NewDocName.docx", readStream, true);
                uploadedFile.CheckOut();
                SPListItem listitem = uploadedFile.Item;
                // Details is mapped in document
                listitem["Details"] = "this content will add in document";
                listitem.Update();
                uploadedFile.Update();
                uploadedFile.CheckIn(string.Empty);
                web.AllowUnsafeUpdates = false;
            }
        });
    }
    catch (Exception ex)
    {
        // handle exception here
    }

}

Where I am going wrong.

Any help would be appreciated.

Thanks