How to: Show Add-in User Interface Errors
By default, if an VSTO Add-in attempts to manipulate the Microsoft Office user interface (UI) and fails, no error message is displayed. However, you can configure Microsoft Office applications to display messages for errors that relate to the UI. You can use these messages to help determine why a custom Ribbon does not appear, or why a Ribbon appears but no controls appear.
Applies to: The information in this topic applies to document-level projects and VSTO add-in projects for the following applications: Excel; InfoPath 2013 and InfoPath 2010; Outlook; PowerPoint; Project; Visio; Word. For more information, see Features Available by Office Application and Project Type.
Start the application.
Click the File tab.
In the categories pane, click Advanced.
In the details pane, select Show VSTO Add-in user interface errors, and then click OK.
For Outlook, the Show VSTO Add-in user interface errors checkbox is located in the Developer section of the details pane. For other applications, the checkbox is located in the General section of the details pane.