edit xml document

[ahbenshaut]

I have an XML document that I am trying to update specific nodes but the node attributes seem to get in the way. If I leave the attributes, "xmlns:.." and try to search, i get an error that says the node is nothing BUT if I rename the "xmlns:" to "ns", the search works. why is this?? I am trying to use the XMLDocument since once the change has been made, the file has to be moved to another network folder.
If anyone has a better idea than what I am trying to do, please let me know. The full XML is below as is the code I am trying to use.

<?xml version="1.0" encoding="utf-8" ?>
<soap:Envelope xmlns:xsd= "http:=//sometext/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <fiAPI xmlns="http://sometextr.com" xmlns:ITI="http://www.Wnet.com/" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" xmlns:xenc="http://www.w3.org/2001/xmlenc#" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://sometext.api.com/API.xsd">
    <fiHeader Version="2.2">
    <Service Name="TST1337" Version="10.0">
    <DateTime>2020-01-09T18:08:02-06:00</DateTime>
    <UUID>23e7a103-fa5b-blah-blah-bf18b1068b4b</UUID>
    </Service>
  <Security>
    <AuthenticationMaterial>
      <SignedToken>
        <EncryptedData>
          <CipherData xmlns="http://www.w3.org/2001/04/xmlenc#">
            <CipherValue>anencryptedstring</CipherValue>
          </CipherData>
        </EncryptedData>
      </SignedToken>
    </AuthenticationMaterial>
    <PrincipalID>Prometheus</PrincipalID>
    <TrustRelationship xmlns="http://www.Wnet.com/">TrustedUser</TrustRelationship>
  </Security>
  <Client>
    <VendorID>FNB-AK!</VendorID>
    <AppID>FNB-AK!INST000</AppID>
    <OrgID>00</OrgID>
    <SessionID></SessionID>
  </Client>
  <DataSource>
    <URI>TEST</URI>
  </DataSource>
</fiHeader>
<Request Echo="false" TypeOfRequest="GetName">
  <NameID>5371</NameID>
  <GroupName>TEST</GroupName>
  <InstNumber>00</InstNumber>
  <Sequence>1</Sequence>
  <Type>Names</Type>
  <Type>AccountNameRelationships</Type>
</Request>
</fiAPI>
  </soap:Body>
</soap:Envelope>

       Dim MyXML As New XmlDocument()
        MyXML.Load("..\..\FNBAXMLFile.xml")
        Dim MyXMLNode As XmlNode = MyXML.SelectSingleNode("/fiAPI/Security/AuthenticationMaterial/SignedToken/EncryptedData/CipherData/CipherValue")
        If MyXMLNode IsNot Nothing Then
            MyXMLNode.ChildNodes(0).InnerText = "CHANGED"
            MyXML.Save("C:\Temp\XmlTest.xml")
        Else
            MessageBox.Show("node is Nothing")
        End If ' Save the Xml.