Deserializing a string XML and error:There is an error in XML document (1, 2)

I need deseriliazing a string XML, but I've a problem.

[XMLRoot]
public class OP
{
    [XmlElement]
    public string Auth;
    [XmlElement]
    public string User;
    [XmlElement]
    public string Password;
    [XmlElement]
    public string Client;
    [XmlElement]
    public string DownloadCode;
    [XmlElement]
    public string PartNumber;
    [XmlElement]
    public int FlexPO;
    [XmlArray]
    public string Terminals;
    [XmlElement]
    public string User;            
}

public void Test()
{
    var serializer = new XmlSerializer(typeof(OP));
    OP result;

    using (TextReader reader = new StringReader(XML))
    {
        result = (OP)serializer.Deserialize(reader);
    }

}

This is code and this is the XML:

<CreateManufactoryOrder xmlns="http://tempuri.org/">
    <op>
        <Auth>
            <User>User</User>
            <Password>Password</Password>
        </Auth>
        <Client>01425787000104</Client>
        <DownloadCode>0460.0001</DownloadCode>
        <PartNumber>M268-773-C4-BRA-3</PartNumber>
        <FlexPO>887614_364</FlexPO>
        <Terminals>
            <String>529-995-835</String>
            <String>529-995-836</String>
            <String>529-995-837</String>
            <String>529-995-838</String>
        </Terminals>
    </op>
</CreateManufactoryOrder>

So, when I debug the code return error: There is an error in XML document (1, 2). I already try change the code in much ways, but nothing did run.