Loops and operators

Hi,
I have a Do-While loop that works OK, until I change some of the If conditions from a field value = 1 to the same field value >=1.
Here is the code:
With rstNames
.MoveFirst
For intCount = 1 To .RecordCount
If .Fields("GPFnWords").Value = 1 And .Fields("PFnWords") = 1 And .Fields("FnTotalMatch") = "N" Then
i = 0
Do
.Edit
.Fields("FnLeftRight1_1") = i
.Update
i = i + 1
Loop While Left(.Fields("GPFn1"), i) = Left(.Fields("PFn1"), i)
End If

Why if I change .Fields("GPFnWords").Value >= 1, does the loop no longer work at i = i+1?

Thankyou