Encoding XML in Vb.net for SOAP Web Service

Hey all I am trying to get this code below to be encoded into UTF8 but it seems to have an error when doing so:

Dim myStringWriter As New StringWriter()
Dim writer As XmlTextWriter = New XmlTextWriter(myStringWriter)
Dim settings As New XmlWriterSettings()

Private Function getDetails() As String
    writer.Formatting = Formatting.Indented
    settings.Encoding = System.Text.Encoding.UTF8
    settings.Indent = True
    settings.ConformanceLevel = ConformanceLevel.Document
    writer = XmlWriter.Create(myStringWriter, settings)        
    getResults(Searcher.FindAll, Searcher)

      'more code here....

    'write out XML
    writer.Flush()
    myXmlString = myStringWriter.ToString()
    myStringWriter.Close()
    writer.Close()
End Function

Private Sub getResults(ByVal results As SearchResultCollection, ByVal Searcher As DirectorySearcher)
    writer.WriteStartDocument(True)
    writer.Formatting = Formatting.Indented
    writer.Indentation = 2
    writer.WriteStartElement("EmployeeInformation")

        'more code here....
    writer.WriteEndElement()
    writer.WriteEndElement()
    writer.WriteEndDocument()
End Sub

The error is:

Additional information: Unable to cast object of type 'System.Xml.XmlWellFormedWriter' to type 'System.Xml.XmlTextWriter'.

On the line:

writer = XmlWriter.Create(myStringWriter, settings)

without defining the Encode.UTF8 it works fine but puts this as the XML string:

<?xml version="1.0" encoding="utf-16" standalone="yes"?>

Which should be:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>

I'm not quite sure how to go about fixing this so any help would be great!