XslTransform is removeing tag

Hello Experts
first time i try to use this so here goes:

I have made a tiny program in VB.net that takes an XML file and apply an XSTL to that file.
the problem is that whenever i try to run the XSLT that looks like:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" exclude-result-prefixes="xsi">
      <xsl:output method="xml" encoding="UTF-8" doctype-system="sample.dtd"/>
      <xsl:template match="/data">
            <data>
                  <xsl:for-each select="dbo.Proever">
                        <dbo.Proeve>
                              <xsl:for-each select="@proeveID">
                                    <proeveID>
                                          <xsl:value-of select="."/>
                                    </proeveID>
......snip
                                          <xsl:for-each select="@metaGruppe">
                                                <metaGruppe>
                                                      <xsl:value-of select="."/>
                                                </metaGruppe>
                                          </xsl:for-each>
                                    </dbo.RNR>
                              </xsl:for-each>
                        </dbo.Proeve>
                  </xsl:for-each>
            </data>
      </xsl:template>
</xsl:stylesheet>

its a rather long xslt file so i have not pasted it all. the problem is that after running this code:

    Public Sub ReadTransformWrite()
        Try
            Dim xpathdocument As New XPathDocument(OpenFileDialog1.FileName)

            Dim xslt As New XslTransform
            xslt.Load(OpenFileDialog2.FileName)

            Dim writer As New XmlTextWriter(SaveFileDialog1.FileName, System.Text.Encoding.UTF8)
            writer.Formatting = Formatting.Indented

            xslt.Transform(xpathdocument, Nothing, writer, Nothing)
            writer.Close()
            Label1.Text = "Processing complete"
        Catch e As Exception
            Label1.Text = "Processing Aborted due to Error"
        End Try
    End Sub

the program output looks like this:

<data>
  <dbo.Proeve>
    <proeveID>1498</proeveID>
    <Analysenavn>C'-funktion, C3, C4, C5, C3 nephr.fact.</Analysenavn>
    <Artikelnr>48579</Artikelnr>

and it have not written out the the <?xml version="1.0" encoding="UTF-8"?> that the output should have started with.

i am quite boggled by this and cant find out why this is so. i could ofcource rewrite the output file and just hardcode the <?xml version="1.0" encoding="UTF-8"?> at the top but i would like to make the program generic so its really not an option.

Thank you for your time
Philip