GetFullFolderName throws COMException constantly in Outlook 2016

Add-in Express™ Support Service
That's what is more important than anything else

GetFullFolderName throws COMException constantly in Outlook 2016
Constant COMExceptions even with empty add-in project / fresh install 
Dave Thompson




Posts: 13
Joined: 2017-11-16
I'd just like to preface this post with the disclaimer that I've been using Add-in express for about 1 week, so please be patient (especially if I'm doing something stupid). The following issue has been distilled to a very simple form,
initially it was detected and tested under various Outlook configurations with the same result.



Here's my dev/environment info

Windows 10 Pro - 64 Bit - x64 base processor - 16GB ram
Visual Studio Community 2015 - Version 14.0.25431.01 Update 3 [run as administrator]
ADX COM Add-In Project - Visual Basic - Minimum supported Office:2013, Only Outlook
adxloader.dll version 8.7.4430.0 / adxLoader64.dll version 8.7.4430.0
Outlook 2016 - 2016 MSO (16.0.8625.2121) 32-bit
Outlook Profile - Brand new + 1 brand new O365 exchange email account
Outlook COM Add-in - 'MyAddInProject' [enabled]
Outlook COM Add-in - 'Microsoft Access Outlook Add-in for Data Collection and Publishing' [disabled]
Outlook COM Add-in - 'Microsoft Exchange Add-in' [enabled]
Outlook COM Add-in - 'Microsoft SharePoint Server Colleague Import Add-in' [disabled]
Outlook COM Add-in - 'OneNote Notes about Outlook Items' [enabled]
Outlook COM Add-in - 'Outlook Social Connector 2016' [disabled]



Steps I can take to recreate and observe the issue

In my Visual Studio Exception Settings I checked 'System.Runtim.InteropServices.COMException' under 'Break When Thrown'

I add the following lines of code AddinModule by clicking into the 'AddinStartupComplete' Event through the AddinModule designer:


Private Sub AddinModule_AddinStartupComplete(sender As Object, e As EventArgs) Handles MyBase.AddinStartupComplete
        Debug.Write("Startup Complete")
    End Sub


I rebuild my project and register via right click MyAddInProject->Add-In Express->Register, and I receive confirmation of successful add-in registration.

I run Outlook and the add-in via the 'Start' button in Visual Studio. Immediately the following 3 COMExceptions are thrown


Exception detail:

Exception thrown: 'System.Runtime.InteropServices.COMException' in mscorlib.dll

Additional information: Unknown name. (Exception from HRESULT: 0x80020006 (DISP_E_UNKNOWNNAME))


Call Stack:
> AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.GetFullFolderName(object folder, bool clearFolderInterface) Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.Install() Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.AddinExpress.MSO.IDTExtensibility2.OnStartupComplete(ref System.Array custom) Unknown

Exception detail:

Exception thrown: 'System.Runtime.InteropServices.COMException' in mscorlib.dll

Additional information: Unknown name. (Exception from HRESULT: 0x80020006 (DISP_E_UNKNOWNNAME))

Call Stack:
> AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.GetFullFolderName(object folder, bool clearFolderInterface) Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_BaseLogic.DoExplorerFolderSwitch() Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_BaseLogic.DoExplorerActivate() Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorersEvents_SinkHelper.DoNewExplorer(object sender, object explorer) Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.AddinExpress.MSO.IDTExtensibility2.OnStartupComplete(ref System.Array custom) Unknown
[AppDomain Transition]


Exception detail:

Exception thrown: 'System.Runtime.InteropServices.COMException' in mscorlib.dll

Additional information: Unknown name. (Exception from HRESULT: 0x80020006 (DISP_E_UNKNOWNNAME))

Call Stack:
> AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.GetFullFolderName(object folder, bool clearFolderInterface) Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_BaseLogic.DoExplorerFolderSwitch() Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_10_SinkHelper.AddinExpress.MSO.IExplorerEvents_10.FolderSwitch() Unknown
[Native to Managed Transition]
[Managed to Native Transition]
[Native to Managed Transition]




At this point any folder I click on throws the following exception



Exception detail:

Exception thrown: 'System.Runtime.InteropServices.COMException' in mscorlib.dll

Additional information: Unknown name. (Exception from HRESULT: 0x80020006 (DISP_E_UNKNOWNNAME))

Call Stack:
> AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.GetFullFolderName(object folder, bool clearFolderInterface) Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_BaseLogic.DoExplorerFolderSwitch() Unknown
AddinExpress.MSO.2005.dll!AddinExpress.MSO.ADXAddinModule.OlExplorerEvents_10_SinkHelper.AddinExpress.MSO.IExplorerEvents_10.FolderSwitch() Unknown
[Native to Managed Transition]
[Managed to Native Transition]
[Native to Managed Transition]




I've spent the last day or so combing through the forum here and have tried a few things including

  • Deleting the .ost - https://www.add-in-express.com/forum/read.php?FID=5&TID=12180
  • Using a different computer
  • Trying only an IMAP Account
  • Trying only a POP Account
  • Trying only an Office 365 Exchange Account
  • Trying several accounts of varying types
  • Completely removing the outlook profile and using a brand new one
  • Using SCANPST.EXE




Aside from the messages in my Visual Studio console I do see the warnings in the COM Addin management dialog that tell me this add-in causes outlook to load slowly.

Any suggestions at this point would be welcome, thanks in advance!
Posted 16 Nov, 2017 12:43:45 Top
Andrei Smolin


Add-in Express team


Posts: 15208
Joined: 2006-05-11
Hello Dave,

What AddinExpress.MSO.2005.dll build does your add-in reference?

Regards from Belarus (GMT+3),

Andrei Smolin
Add-in Express Team Leader
Posted 17 Nov, 2017 03:51:04 Top
Dave Thompson




Posts: 13
Joined: 2017-11-16
Hi Andrei,

The version of my AddinExpress.MOS.2005.dll file I'm seeing is 8.7.4430.0

I obtained that version by going to the ~/bin/ folder for the project in Windows Explorer, then right clicking on the .dll file ->Properties->Details
Posted 20 Nov, 2017 11:03:37 Top
Andrei Smolin


Add-in Express team


Posts: 15208
Joined: 2006-05-11
Hello Dave,

Please unregister the add-in and start Outlook from Visual Studio. In Outlook note the Outlook folder opened at startup: Does this folder belong to an Exchange mailbox? PST? Other? Will the issue persist if you change the startup folder?

Also, please uncheck all other add-ins in the COM Add-ins dialog.

Regards from Belarus (GMT+3),

Andrei Smolin
Add-in Express Team Leader
Posted 21 Nov, 2017 06:03:12 Top
Dave Thompson




Posts: 13
Joined: 2017-11-16
Hi Andrei,

I unchecked all other add-ins, after I unregister the add-in and re-launch Outlook the errors stop. Re-registering the add-in (all other add-ins are still unchecked) and re-launching Outlook causes the errors to resume.

I tested the following startup folders before un-registering the add-in, while the add-in was unregistered, and after re-registering the add-in. The result was the same under all of these conditions (all other add-ins were unchecked).


  • The startup folder is an Exchange Mailbox (specifically the inbox on a developer .onmicrosoft.com account), errors persist.
  • I change the startup folder to another folder (also belong to the same Exchange Mailbox) the issue persists.
Posted 21 Nov, 2017 18:03:18 Top
Andrei Smolin


Add-in Express team


Posts: 15208
Joined: 2006-05-11
Hello Dave,

Will I be able to access your PC remotely in three-four hours (I'm a bit busy now)? If yes, I suggest using TeamViewer; in this case you'll need to send me your session ID and password. I'll let you know when I'm available.

Regards from Belarus (GMT+3),

Andrei Smolin
Add-in Express Team Leader
Posted 22 Nov, 2017 04:41:06 Top
Dave Thompson




Posts: 13
Joined: 2017-11-16
Hi Andrei,

I'll be available starting at 6:15 p.m. in you time zone (GMT +3). Approx 1 hr 15 minutes from this post. I'll send you a direct message with ID and password shortly!
Posted 22 Nov, 2017 09:32:19 Top
Andrei Smolin


Add-in Express team


Posts: 15208
Joined: 2006-05-11
Hello Dave,

Writing from home. Could you please send me the InitializeComponent() method which is called from the constructor of the add-in module to the support email address? If the add-in is simple, please send me the whole project.

Regards from Belarus (GMT+3),

Andrei Smolin
Add-in Express Team Leader
Posted 22 Nov, 2017 12:12:23 Top
Dave Thompson




Posts: 13
Joined: 2017-11-16
Hi Andrei,

I just sent an email with a link to the project files

Thank you!
Posted 22 Nov, 2017 12:32:03 Top
Andrei Smolin


Add-in Express team


Posts: 15208
Joined: 2006-05-11
Thank you, Dave.

I can't reproduce the issue on our side. Could you please re-create the .OST file as they suggest at https://support.office.com/en-us/article/Repair-Outlook-Data-Files-pst-and-ost-25663bc3-11ec-4412-86c4-60458afc5253?

Regards from Belarus (GMT+3),

Andrei Smolin
Add-in Express Team Leader
Posted 23 Nov, 2017 06:17:08 Top