Deserialize DatagridView

I am trying to deserialize from an xml file to a datagridview, but I think I did something wrong. VS is throwing a System Invalid Operation Exception on (2,2). Can somebody tell me what I did wrong here?

results.xml

<?xml version="1.0" encoding="utf-8"?>
<DataTable>
<xs:schema id="NewDataSet" xmlns="" xmlns:xs="http://ift.tt/tphNwY"    xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
<xs:element name="NewDataSet" msdata:IsDataSet="true" msdata:MainDataTable="data" msdata:UseCurrentLocale="true">
  <xs:complexType>
    <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="data">
        <xs:complexType>
          <xs:sequence>
            <xs:element name="col1" type="xs:string" minOccurs="0" />
            <xs:element name="col2" type="xs:string" minOccurs="0" />
            <xs:element name="col3" type="xs:string" minOccurs="0" />
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:choice>
  </xs:complexType>
</xs:element>
</xs:schema>
<diffgr:diffgram xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" xmlns:diffgr="urn:schemas-microsoft-com:xml-diffgram-v1">
<DocumentElement>
  <data diffgr:id="data1" msdata:rowOrder="0" diffgr:hasChanges="inserted">
    <col1>r1c1</col1>
    <col2>r1c2</col2>
    <col3>r1c3</col3>
  </data>
  <data diffgr:id="data2" msdata:rowOrder="1" diffgr:hasChanges="inserted">
    <col1>r1c2</col1>
    <col2>r1c2</col2>
    <col3>r1c2</col3>
  </data>
</DocumentElement>
</diffgr:diffgram>
</DataTable>

Deserialization code:

  public void loadXMLfile()//runs on application start
    {
    UserCollection users = null;

    XmlSerializer serializer = new XmlSerializer(typeof(UserCollection));

    StreamReader reader = new StreamReader(filePath);
    users = (UserCollection)serializer.Deserialize(reader);
    reader.Close();
    // finally bind the data to the grid
    dg1.DataSource = users.User;
    }

    [Serializable()]
    public class DeserializeData
    {
        [System.Xml.Serialization.XmlElement("col1")]
        public string col1 { get; set; }

        [System.Xml.Serialization.XmlElement("col2")]
        public string col2 { get; set; }

        [System.Xml.Serialization.XmlElement("col3")]
        public string col3 { get; set; }
    }

    [Serializable()]
    [System.Xml.Serialization.XmlRoot("DocumentElement")]
    public class UserCollection
    {
        [XmlArray("data")]
        [XmlArrayItem("data", typeof(DeserializeData))]
        public DeserializeData[] User { get; set; }
    }

serialize code (button):

private void saveDatagrid_Click(object sender, EventArgs e)
    {
        XmlSerializer ser = new XmlSerializer(typeof(DataTable));
        DataTable dt = new DataTable("data");

        dt.Columns.Add("col1");//I will just iterate through the datagridview to populate a row when the code works correctly
        dt.Columns.Add("col2");
        dt.Columns.Add("col3");
        string[] row = { "r1c1", "r1c2", "r1c3" };
        string[] row1 = { "r2c1", "r2c2", "r2c3" };
        dt.Rows.Add(row);
        dt.Rows.Add(row1);
        TextWriter writer = new StreamWriter(filePath);
        ser.Serialize(writer, dt);
        writer.Close();
    }