The strange case of sporadic COMException 0x800A01A8 calling CommandBarButton.Delete from a Visual Studio add-in

I don’t have an answer to this strange case, but after 4+ years getting reports from users, I will write about it just in case someone can post a solution.

When using a temporary user interface (not a permanent one), add-ins typically add CommandBarButtons to commandbars using Command.AddControl when loaded. When the add-in is unloaded, it must remove its buttons calling CommandBarButton.Delete. You can see a sample in the following article of mine: HOWTO: Adding buttons, commandbars and toolbars to Visual Studio .NET from an add-in

The problem is that sometimes you get COMException 0x800A01A8 when calling CommandBarButton.Delete. There are some facts about this problem:

  • It happens very sporadically (I have received less than 20 user reports in all these years).
  • When I ask the users if the problem is reproducible, they always answer that no, that the add-in unloads fine next time.

So the occurrence is really really tiny and it is not a bug in the code of the add-in since it works fine almost always, but nonetheless I would like to erradicate it.

Searching the Web, it seems that this problem appears more commonly with add-ins for Office, but no forum seems to deal with Visual Studio add-ins or provides an answer.

A couple of years ago I posted in the MSDN Forum:

To Microsoft: Sporadic COM exceptions adding/removing commandbars and buttons from Visual Studio add-ins

In that post I exposed three reproducible cases of COM Exceptions, but I mentioned that there were more COM exceptions. Reviewing the user reports in my e-mail system, I think that in fact there is only a non-reproducible COMException 0x800A01A8 and it happens always calling CommandBarButton.Delete.

Craig Skibo (former member of the Visual Studio extensibility team) answered to that post but since I posted 3 reproducible cases and 1 non-reproducible case the discussion was a bit messed and in the part that dealed with CommandBarButton.Delete he argued that buttons created with Command.AddControl shouldn’t be destroyed calling CommandBarButton.Delete, but IMHO he is wrong or his workarounds are not really workarounds.

So, at this point I don’t know it I should ignore that exception because I am not sure if the COM exception is caused because the button is not already there (it would be OK to ignore the exception) or if I would get a duplicated button the next time that the add-in is loaded (in this case I would like to notify the previous exception to know why I am getting a duplicated button).

Anyone is experiencing this problem? You can either post a comment or contact me by e-mail.

Finally, wouldn’t be nice to be able to debug the code of Microsoft.VisualStudio.CommandBars.dll when the exception is thrown? Or better yet, a managed IDE where the menus and toolbars are no longer based on Office COM-based commandbars?

Update (February 3, 2009). See More on the The strange case of sporadic COMException 0x800A01A8 calling CommandBarButton.Delete from a Visual Studio add-in (solved)

2 thoughts on “The strange case of sporadic COMException 0x800A01A8 calling CommandBarButton.Delete from a Visual Studio add-in”

  1. I experience the same problem with office add-in and it occures always when i use CommandBarButton.Delete(Missing.Value) during OnDisconnection event on both Microsoft Office 2003 and 2007

  2. I get the same exact problem in Outlook 2003 in my OnBeginShutdown method.
    here’s the code that throws an exception:

    public void OnBeginShutdown(ref Array custom)

    this.toolbarButton = null;
    catch (Exception ex)


    And the definition of the “toolbarButton” is such:
    private CommandBarButton toolbarButton;

Comments are closed.