ONode is set to Nothing, but why and how to fix it?

I am trying to develop a token (in this case a piece of code that runs inside a larger VBScript) that returns information from XML supplied by third party software to a word plugin using bookmarks to provide parameters for the tokens.

So here's what's going on,

XmlDoc.SetProperty "SelectionLanguage", "XPath"

ReturnData = vbNullString

Public Function GetParameterXml()
    GetParameterXml = _
    "<Parameters>" & _
        "<Parameter Value='Last_Hearing' Code='L' Description='Last_Hearing' Type='Combo'>" & _
            "<Options>" & _
                "<Option Code='' Description='True' Value='True' />" & _
                "<Option Code='' Description='False' Value='False' />" & _
            "</Options>" & _
        "</Parameter>" & _
    "</Parameters>"     
End Function

Dim oNode : Set oNode = XmlDoc.SelectSingleNode("/Record/CelloXml/Integration/Case/Hearing/Setting/CourtroomMinutes/Comment")
Dim lastHearing : Set lastHearing = Parameters.Item( BookMark, "Last_Hearing" )     

If IsNull(lastHearing) Then
    lastHearing = False
End If
stop
If lastHearing.Value = "True" Then
    Dim dateNodes : Set dateNodes = XmlDoc.SelectNodes("/Record/CelloXml/Integration/Case/Hearing/Setting/HearingDate")
    Dim mostRecentHearingDate
    Dim dateNode
    Dim todaysDate
    todaysDate = Date

    Dim dateList : Set dateList = CreateObject("System.Collections.ArrayList")
    For Each dateNode In dateNodes
        dateList.Add CDate(dateNode.Text)
    Next
    dateList.Sort()

    Dim tempDate
    For Each tempDate In dateList
        If tempDate < todaysDate Then
            mostRecentHearingDate = tempDate
        End If
    Next
    mostRecentHearingDate = CStr(mostRecentHearingDate)
    Set oNode = XmlDoc.selectSingleNode("/Record/CelloXml/Integration/Case/Hearing/Setting[HearingDate/text()='" & mostRecentHearingDate & "']/CourtroomMinutes/Comment")
End If

If Not oNode Is Nothing Then
    ReturnData = oNode.text
Else
    ReturnData = vbNullString
End If

      

        
        
        
      

    

Everything works the way I want, as long as

Set oNode = XmlDoc.selectSingleNode("/Record/CelloXml/Integration/Case/Hearing/Setting[HearingDate/text()='" & mostRecentHearingDate & "']/CourtroomMinutes/Comment")

      

        
        
        
      

    

I needed dateList

to store dates (or literary dates) because I assumed I was getting a bad sort if I tried to sort dates as a string rather than an actual date, so I converted the text from node to date (or date) and added it todateList

When I finished all calculations, I needed a string to run in my XPath, if I hard copy the date (as string {08/05/2014}) into the XPath query, it works, but when I convert mostRecentHearingDate

to string with CStr

then oNode

set to Nothing

node exists and contains data

So,

• Why is this happening?
• How do I get it to function the way it seems to me?