Upload file web method with c#

Upload.cs

public bool UploadFile(string FileName, byte[] buffer, long Offset)
    {
        bool retVal = false;
        try
        {
            // setting the file location to be saved in the server. 
            // reading from the web.config file 
            string FilePath =
            //Path.Combine(ConfigurationManager.AppSettings["upload_path"], FileName);
            //WebConfigurationManager.AppSettings["PFUserName"].ToString()
            Path.Combine(System.Web.Hosting.HostingEnvironment.MapPath
                        ("~/TransientStorage/"), FileName);
            ;
            if (Offset == 0) // new file, create an empty file
                File.Create(FilePath).Close();
            // open a file stream and write the buffer. 
            // Don't open with FileMode.Append because the transfer may wish to 
            // start a different point
            using (FileStream fs = new FileStream(FilePath, FileMode.Open,
            FileAccess.ReadWrite, FileShare.Read))
            {
                fs.Seek(Offset, SeekOrigin.Begin);
                fs.Write(buffer, 0, buffer.Length);
            }
            retVal = true;
        }
        catch (Exception e)
        {
            //sending error to an email id
        }
        return retVal;
    }