Enter Key To Trigger CommandButton Click Event

I am working with a large legacy file/program which has a lot of issues. Foremost, and unfortunately this cannot be changed, is that all of the controls were placed directly on the worksheets instead of on Userforms. The actual code from the legacy file is excessively complicated, so I created this simple example. Sheet1 has one textbox and one command button. Sheet 2 is blank. I want to be able to click the command button or use the Enter key on the command button, to trigger the Click Event. Clicking works fine. When using Enter, if Sheet2.Activate is commented, everything works fine. If Sheet2.Activate is executed, then Excel crashes.

Private Sub TextBox1_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)
Dim bBackwards As Boolean
Select Case KeyCode
'Only look for tab, return, down arrow, up arrow
Case vbKeyTab, vbKeyReturn, vbKeyDown, vbKeyUp
Application. ScreenUpdating = False
'Do we need to go back to previous control
bBackwards = CBool(Shift And 1) Or (KeyCode = vbKeyUp)
If bBackwards Then TextBox1.Activate Else CommandButton1.Activate
Application.ScreenUpdating = True
End Select
End Sub
Private Sub CommandButton1_KeyDown(ByVal KeyCode As MSForms.ReturnInteger, ByVal Shift As Integer)
Dim bBackwards, bForwards As Boolean
Select Case KeyCode
Case vbKeyTab, vbKeyReturn, vbKeyDown, vbKeyUp
Application.ScreenUpdating = False...................