Out o range error vba code finding last empty row for

Sub transferorderdata()
Dim wkbor, wkbvl, wkbysd, wkbtr As Workbook
Dim wknm, wknm1, wknm2  As String

wknm2 = "C:\vbproject\tracker\ysdflow2.xlsx"
wknm = "d:\a.xlsx" '-------Open order
wknm1 = "d:\SAMPLE.xlsx" '------tracker file
Set wkbor = Workbooks.Open(wknm)
Set wkbtr = Workbooks.Open(wknm1)
Dim irowor, irowtro, irowtrs As Integer
Dim i, j As Integer
Dim selor, seltro As String
Dim blnor As Boolean
Dim sample As String

'__________________Ordering Compare_________________
irowor = wkbor.Sheets("Sheet1").Cells(Rows.Count, 1).End(xlUp).Offset(1, 0).Row
irowtro = wkbtr.Sheets("Ordering").Cells(Rows.Count, 2).End(xlUp).Offset(1, 0).Row