Deserialize -> Serialize produces invalid XML file

Hi,

I'm trying to read and write .gpx file produced by an Garmin handheld device. Everything is working fine except the output file is invalid according to http://www.validome.org/xml/validate/ -validator.

Even if I just read the file into a dataset and write it immediately to another file without making any changes to data, I get invalid output. Data itself is valid but something gets wrong with header (schema definitions etc.)

Public Sub TryXmlDocument()
     Dim xmlFile As XmlReader
     Dim ds as New DataSet
     xmlFile = XmlReader.Create("filename.gpx", New XmlReaderSettings())
     ds.ReadXml(xmlFile, XmlReadMode.Auto)
     ds.WriteXml("filename_new.gpx")
End Sub

Anyone out there with solution?