Excel VBA Copy Row Intermittent Crash

I have a push button in a merged cell which copies all the rows of the merged cells and inserts them below those rows. The code works fine for the majority of the time. However, on some occasions the code causes Excel to close without warning. With some debugging I have identified the row it does this on is the insert row line. Do you know what might cause this crash? My code (with irrelevant parts removed) is below:

Sub CopyRows()

Application.ScreenUpdating = False
Application.EnableEvents = False
Application.CutCopyMode = True

Dim Top As Integer
Dim Bottom As Integer
Dim NumRows As Integer

ActiveSheet.Buttons(Application.Caller).TopLeftCell.Select

NumRows = ActiveCell.MergeArea.Rows.Count
Top = ActiveCell.Row
Bottom = NumRows + Top - 1

ActiveSheet.Rows(Top & ":" & Bottom).EntireRow.Copy
ActiveSheet.Range("A" & Bottom + 1).EntireRow.Insert shift:=xlDown '<<<< this is where it crashes
Application.CutCopyMode = False
Sleep 100

Top = Bottom + 1
Bottom = NumRows + Top - 1
ActiveSheet.Range("D" & Top & ":D" & Bottom).ClearContents
Sleep 100

Application.ScreenUpdating = True
Application.EnableEvents = True

End Sub