TextWriter not writing everything

I have a webservice that takes a base64 encoded string and converts it to xml, and then writes it out to a file.

Here is the code that creates the base64 string:

MemoryStream memStream = new MemoryStream();
                        TextWriter writer = new StreamWriter(memStream);
                        TextReader reader = new StreamReader(this.txtPath.Text);
                        writer.Write(reader.ReadToEnd());
                        writer.Close();
                        param = Convert.ToBase64String(memStream.ToArray();


And here is the code that reads the base64 string back to text (xml):

public string Add(string Base64Binary)
            {
                  try
                  {
                        MemoryStream memStream = new MemoryStream(Convert.FromBase64String(Base64Binary));
                        TextReader reader = new StreamReader(memStream);
                        string temp = reader.ReadToEnd();
                        FileStream strm = new FileStream(Server.MapPath(Guid.NewGuid().ToString() + ".xml"), FileMode.Create, FileAccess.Write);
                        TextWriter writer = new StreamWriter(strm);
                        writer.Write(temp);
                        strm.Close();
                        return "Ack";
                  }

The thing is: The file, when I open it, seems to be truncated! Have any of you guys run into this problem before, and know what's going on? Thanks!