VSTO Addin not visible in Outlook COM Addin

Question

I have an Outlook Add-in, which is not visible in Outlook COM Add-ins and Disabled items windows. The Add-in was working fine few days ago with both debug using Visual studio mode and Setup created by Windows installer project.

I checked for correct registry being created, and it is correct.

Also, no error is thrown at VS console while debugging. So idk what is the actual error here.

I also tried to run VSTO Deployment file directly from bin folder, but it gave me some error:

Name: From: file:///C:/Users/User/source/repos/MyOutlook/MyOutlookAddin/bin/Debug/MyOutlookAddin.vsto

************** Exception Text ************** System.Deployment.Application.DeploymentDownloadException: Downloading file:///C:/Users/User/source/repos/MyOutlook/MyOutlookAddin/bin/Debug/MyOutlookAddin.vsto did not succeed. ---> System.Net.WebException: Could not find a part of the path 'C:\Users\User\source\repos\MyOutlook\MyOutlookAddin\bin\Debug\MyOutlookAddin.vsto'. ---> System.Net.WebException: Could not find a part of the path 'C:\Users\User\source\repos\MyOutlook\MyOutlookAddin\bin\Debug\MyOutlookAddin.vsto'. ---> System.IO.DirectoryNotFoundException: Could not find a part of the path 'C:\Users\User\source\repos\MyOutlook\MyOutlookAddin\bin\Debug\MyOutlookAddin.vsto'. at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost) at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, String msgPath, Boolean bFromProxy) at System.Net.FileWebStream..ctor(FileWebRequest request, String path, FileMode mode, FileAccess access, FileShare sharing, Int32 length, Boolean async) at System.Net.FileWebResponse..ctor(FileWebRequest request, Uri uri, FileAccess access, Boolean asyncHint) --- End of inner exception stack trace --- at System.Net.FileWebResponse..ctor(FileWebRequest request, Uri uri, FileAccess access, Boolean asyncHint) at System.Net.FileWebRequest.GetResponseCallback(Object state) --- End of inner exception stack trace --- at System.Net.FileWebRequest.EndGetResponse(IAsyncResult asyncResult) at System.Net.FileWebRequest.GetResponse() at System.Deployment.Application.SystemNetDownloader.DownloadSingleFile(DownloadQueueItem next) --- End of inner exception stack trace --- at Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.GetManifests(TimeSpan timeout) at Microsoft.VisualStudio.Tools.Applications.Deployment.ClickOnceAddInDeploymentManager.InstallAddIn()

Can anybody tell me what is the issue here and how I can solve it?

Do you see Outlook create anything on the startup in the Windows Even log? Have you tried to use ProcMon to see if your add is being loaded? Are there any errors (missing dlls etc.)? — Dmitry Streblechenko
Hello @DmitryStreblechenko, I just found the step from where the issue is getting generated. It is the Application Settings. I introduced some new properties inside Rightclick on project -> Properties -> Settings, and just after that my addin is not visible in Outlook. Removing those properties again is not working too. Do you have any idea, where it got stuck? — Ank Raw
Again, does Outlook show any errors in the event log on startup? — Dmitry Streblechenko
No, not getting any error in event log. Also, I used process explorer and found that outlook is not loading my Add-in dll. — Ank Raw

Eugene Astafiev Eugene Astafiev · Accepted Answer · 2020-05-26T14:46:27

It seems you didn't create an MSI installer correctly, or just missed some steps. The Deploy an Office solution by using Windows Installer article explains how to create a Windows Installer for your Office solution by using Visual Studio. So, make sure that you did everything listed in the articles.

System.Deployment.Application.DeploymentDownloadException: Downloading file:///C:/Users/User/source/repos/MyOutlook/MyOutlookAddin/bin/Debug/MyOutlookAddin.vsto did not succeed. ---> System.Net.WebException: Could not find a part of the path

The exception states you deployed an add-in using the ClickOnce technology. You shouldn't really combine all technologies and decide to use a single one - ClickOnce or MSI. Otherwise, you will trap into situations like that. If you decide to follow up with ClickOnce, see Deploy an Office solution by using ClickOnce for more information.

Finally, to troubleshoot issues with add-in deployments take a look at the Troubleshoot Office solution deployment page.

VSTO Addin not visible in Outlook COM Addin

1 Answers