Writing this code to help analyze and re-organize our e-mail promotions and every time I try to run the script, it just freezes up Excel (infinite loop somewhere?). It's pulling data from another sheet ("Promos") in the same workbook.

Code:
Sub Update_Campaign_Breakdown()
Dim rownum As Integer
Dim campaign As String
Dim newrows As Integer
Dim i As Integer
rownum = 2
Do Until IsEmpty(Sheets("Promos").Cells(rownum,
...