MSXML2 appendChild method fails in debugger only

I have a method that will dynamically build an XML schema based on schema fragments provided by upstream clients.  The mergeSchema method takes the various fragments each time this method is called and merges them into the fullSchema .  At this point, the method is not eliminating duplicates, (that's what I'm trying to code)

On the line marked by '*****, I'm getting an error message when I work in the VB debugger, namely "The parameter is invalid".  But when I compile it and run, the same line does its work and executes.  Is there a way to work around this and still get the same behavior?


Private Sub IToldSchemaMerger_mergeSchema(schemaChanges As MSXML2.IXMLDOMNode, fullSchema As MSXML2.IXMLDOMNode, ByVal schemaID As Long)
    Dim currentItem As MSXML2.IXMLDOMElement
    Dim dupe As MSXML2.IXMLDOMNode
    Dim fullyMatchingNode As MSXML2.IXMLDOMNode
    Dim l_schemaBase As MSXML2.IXMLDOMNode
    Dim l_fullSchema As MSXML2.IXMLDOMElement
    Dim l_throwAwayElements As MSXML2.IXMLDOMNode
   
    Set dom = CreateObject("MSXML2.DOMDocument")
    m_schemaID = schemaID
    dom.loadXML (fullSchema.xml)

    Set l_throwAwayElements = dom.createNode(NODE_ELEMENT, "THROW_AWAY", vbNullString)
    Set l_schemaBase = schemaChanges.selectSingleNode("/SCHEMA_CHANGES")
    removeNSAttribute l_schemaBase
    Set l_fullSchema = dom.selectSingleNode("/schema")

    'for each complexType in schemaChanges,
    With l_schemaBase.childNodes
        While .length > 0
            Set dupe = duplicateEntry(l_fullSchema, .item(0))

'            if the complexType already exists
             If dupe Is Nothing Then
                'add the complexType to the schema
                l_fullSchema.appendChild .item(0)   '*****
             Else
                'compare more closely and either drop it or alter the complexType name
               Set fullyMatchingNode = identicalNodes(dupe, .item(0))
               If fullyMatchingNode Is Nothing Then
                    'remove the item from the schema additions
                    l_throwAwayElements.appendChild .item(0)
               Else
                    Set currentItem = .item(0)
                    mergeSimilarComplexTypes l_schemaBase, currentItem
                    'Set currentItem = Nothing

               End If
             End If
        Wend
    End With

    removeNSAttribute l_fullSchema

    Set fullSchema = l_fullSchema
End Sub