macro errors out

When running the enclosed macro, I receive a Object variable or With block variable not set, error Line <code> trlen = tr.ChildNodes.Length <code>

any help or suggestions would be appreciated.

Sub RotoWire_Pitchers()
    Dim k As Integer
    Dim trlen As Long
    Dim i As Long
    Dim j As Integer
    Dim tr As Object
    Dim th As Object
    Set XMLHTTP = CreateObject("MSXML2.XMLHTTP")
    Dim XMLHttpRequest As MSXML2.XMLHTTP
    
    Dim URLa As String
    Dim HTMLDoc As HTMLDocument
    'On Error Resume Next
    Application.Calculation = xlCalculationManual
    Application.ScreenUpdating = False
       
       
    Sheets("PITCHER REPORT").Select
    
    URLa = "http://www.rotowire.com/baseball/player_stats.htm?league=3&pos=P&filter=A"
    
    Set XMLHttpRequest = New MSXML2.XMLHTTP
    XMLHttpRequest.Open "GET", URLa, False
    XMLHttpRequest.send
    
    Set HTMLDoc = New HTMLDocument
    HTMLDoc.body.innerHTML = XMLHttpRequest.responseText
    Set tr = HTMLDoc.getElementsByTagName("tbody")(91)
    trlen = tr.ChildNodes.Length
    'Range("A1").Value = trlen
    For i = 1 To trlen - 1
        tdlen = 20
            For j = 0 To tdlen - 1
                Cells(i + 1, j + 2).Value = tr.ChildNodes(i).ChildNodes(j).innerText
                Next j
    Next i
    
 Set tr = Nothing
 Set HTMLDoc = Nothing
 
Application.ScreenUpdating = True
Application.Calculation = xlCalculationAutomatic
End Sub