Error: "Method 'rows' of object '_Global' failed - vba

Question

For some reason even though I am referring to the oSheet variable it is returning the error as if I am referring to a global variable?
PS I am trying to populate a combobox in word with a contractor names from an excel sheet I have created. I searched in google and here, none of the solutions have worked for me unfortunately. I believe the error lies within the For Each statement.
Sub Macro3()
Dim oXL As Excel.Application
Dim oWB As Excel.Workbook
Dim oSheet As Excel.Worksheet
Dim oRng As Excel.Range
Dim ExcelWasNotRunning As Boolean
Dim WorkbookToWorkOn As String
'specify the workbook to work on
WorkbookToWorkOn = "C:\Users\Nathan\Desktop\KTC\VBA Experiment\Excel Files\testExcel.xlsx"
'If Excel is running, get a handle on it; otherwise start a new instance of Excel
On Error Resume Next
Set oXL = GetObject(, "Excel.Application")
If Err Then
ExcelWasNotRunning = True
Set oXL = New Excel.Application
End If
On Error GoTo Err_Handler
'If you want Excel to be visible, you could add the line: oXL.Visible = True here; but your code will run faster if you don't make it visible
'Open the workbook
Set oWB = oXL.Workbooks.Open(FileName:=WorkbookToWorkOn)
'Process each of the spreadsheets in the workbook
For Each oSheet In oXL.ActiveWorkbook.Worksheets
'put guts of your code here
'get next sheet
If oSheet.Cells(Rows.Count, 1).End(xlUp).Row = 1 Then
lastRow = 2
Else
lastRow = oSheet.Cells(Rows.Count, 1).End(xlUp).Row
End If
' For i = 2 To lastRow
' workZonerForm.contracterCMB.AddItem oSheet.Cells(i, 1)
' Next i
MsgBox lastRow
Next oSheet
If ExcelWasNotRunning Then
oXL.Quit
End If
'Make sure you release object references.
Set oRng = Nothing
Set oSheet = Nothing
Set oWB = Nothing
Set oXL = Nothing
'quit
Exit Sub
Err_Handler:
MsgBox WorkbookToWorkOn & " caused a problem. " & Err.Description, vbCritical, _
"Error: " & Err.Number
If ExcelWasNotRunning Then
oXL.Quit
End If
End Sub