XML : XML Deserialization error: xxxxx was not expected

I know there are several posts out there with this topic, but I can't seem to figure out what is the problem here. I have serialized and deserialized xml several times, and never had this error.

The exception message is:

There is an error in XML document (1, 2).

With InnerException:

<InvoiceChangeRequest xmlns=''> was not expected.

XML file I want to deserialize:

  <ns1:InvoiceChangeRequest xmlns:ns1="http://kmd.dk/fie/external_invoiceDistribution">  <CONTROL_FIELDS>      <STRUCTURID>0000000001</STRUCTURID>      <OPERA>GET</OPERA>      <WIID>000050371220</WIID>  </CONTROL_FIELDS>  <HEADER_IN>      <MANDT>751</MANDT>      <BELNR>1234567890</BELNR>  </HEADER_IN>  <ITEMS>      <ITEM_FIELDS_IN>          <BUZEI>001</BUZEI>          <BUKRS>0020</BUKRS>      </ITEM_FIELDS_IN>  </ITEMS>    

Class I'm trying to deserialize to:

  [XmlRoot(Namespace = "http://kmd.dk/fie/external_invoiceDistribution", IsNullable = false)]  public class InvoiceChangeRequest  {      [XmlElement("CONTROL_FIELDS")] public ControlFields Styrefelter;      [XmlElement("HEADER_IN")] public HeaderIn HeaderfelterInd;      [XmlElement("ITEMS")] public Items Linjer;  }    public class HeaderIn  {      [XmlElement("MANDT")] public string Kommunenummer;      [XmlElement("BELNR")] public string RegnskabsbilagsNummer;  }    public class Items  {      [XmlElement("ITEM_FIELDS_IN")] public Itemfield[] ItemfelterInd;  }    public class Itemfield  {      [XmlElement("BUZEI")] public string Linjenummer;      [XmlElement("BUKRS")] public string Firmakode;  }    

Deserialization code:

  XmlSerializer serializer = new XmlSerializer(typeof(InvoiceChangeRequest));  var request = serializer.Deserialize(new StringReader(output)) as InvoiceChangeRequest;