Deserialization error in XML document(1,1)

I have an XML file that I deserialize, the funny part is the XML file is the was serialized using the following code:

enter code here
var serializer = new XmlSerializer(typeof(CommonMessage));
var writer = new StreamWriter("OutPut.txt");
serializer.Serialize(writer, commonMessage);
writer.Close();

And i m trying to deserialized it again to check if the output match the input. anyhow here is my code to deserialize:

var serializer = new XmlSerializer(typeof(CommonMessage));
var reader = new StringReader(InputFileName);
CommonMessage commonMessage = (CommonMessage)serializer.Deserialize(reader);