Personally I would just add an error handler to it. Added screenupdating =false and noticed a bit of a speed improvement he

Sub STEP3TEST()
Application.Wait Now + TimeValue("00:00:03")

Dim Curr_Base As Long
Dim Prev_Base As Long
Dim i As Long
Dim Loop_Count As Long

With Application
.ScreenUpdating = False

On Error GoTo ErrHandle
ActiveWindow.Activate
Loop_Count = Range(Selection, Selection.End(xlDown)).Count
'MsgBox Loop_Count
For i = 3 To Loop_Count
Range("E" & i).Select
Curr_Base = ActiveWindow.ActiveCell
'MsgBox Curr_Base
If (Curr_Base = Prev_Base) Then
ActiveWindow.SelectedSheets.HPageBreaks.Add befo=ActiveCell
End If
Prev_Base = Curr_Base
Next i

ErrorExit:
.ScreenUpdating = True
End With
Exit Sub
ErrHandle:
MsgBox "Limit Reached"
GoTo ErrorExit
End Sub