HELP Getting data from closed workbook using VBA code

Hi,

I'm getting a Run-time error '91': Object variable or With block variable not set

Set wb = Workbooks.Open("T:\Data\LMS Leads Conversion.xlsm", True, True)
' the sheet in this workbook to copy to
With ThisWorkbook.Worksheets("LMS Data")
' read data from the source workbook
'the range to copy to in this workbook-name of sheet to copy FROM-range in closed workbook to copy
.Range("B7", "AR174").Formula = wb.Worksheets("Conversions Summary").Range("C9", "AS176").Formula
End With

I managed to use the same code to copy & paste data from another closed workbook without any errors. Should there be any difference when copying the data from xlsx vs xlsm?