Excel crashes when install an addin - excel

Question

Excel AddIn, .NET 4.0, NetOffice 1.5.1.2, ExcelDNA 1.29, C#
installers calls a xls (install.xls) with VBA as follow
At the end of install.xls, Excel will close.
However, after Excel closes, Excel crashes saying "Excel stops working... please send report to Microsoft" with two buttons, one is "Don't Send", the other is send
This ONLY happens on Windows XP + Excel 2007 or WinXP + Excel 2010.
Also during debug I notice if I replace Application.Wait with MsgBox, then there is no crashes issue at all. I feel there is some kind of timing issue but really has no clue no control.
The issue drives me crazy. Please help. thanks!
Private Sub Workbook_Open()
Dim quit As Integer
Dim added As Boolean
added = Add_Addin
Application.Wait (Now + TimeValue("0:00:02"))
If Workbooks.Count = 1 Then
Application.Wait Now + TimeValue("0:00:03")
Application.quit
Else
Application.Wait Now + TimeValue("0:00:03")
Me.Close
End If
End Sub
Private Function Add_Addin() As Boolean
On Error GoTo ERR_
Dim addinFile As String
addinFile = ThisWorkbook.Path & "\" & "MyAdd-In.xll"
If Len(addinFile) > 0 Then
Dim LEA As AddIn
Set LEA = Application.AddIns.Add(addinFile)
If (Not LEA Is Nothing) Then
LEA.Installed = True
Else
MsgBox "Failed to add XLL"
End If
'If (Application.RegisterXLL(addinFile) = True) Then
' MsgBox "Yeah, succeed registering XLL"
'Else
' MsgBox "Failed to register XLL"
'End If
Else
MsgBox "XLL file not found"
End If
addinFile = ThisWorkbook.Path & "\" & "MyFunc.xla"
If Len(addinFile) > 0 Then
Dim LEA2 As AddIn
Set LEA2 = Application.AddIns.Add(addinFile)
If (Not LEA2 Is Nothing) Then
LEA2.Installed = True
Else
MsgBox "Failed to add xla"
End If
Else
MsgBox "xla file not found"
End If
Add_Addin = True
Exit Function
ERR_:
MsgBox ("Error " & Err.Number & " " & Err.Description)
Add_Addin = False
End Function

Answer 1

I figured it out. I kicked off a web service call asychronously with callback When Excel opens. When the callback of the web service call is executed after Excel is disposed or close, the crash occurred. The callback disbales/enables ribbon buttons based on the result from web service. I fixed it by checking if Excel is null or disposed before doing anything else in the callback.