Use this outline below to enable detailed error messages from Visual Studio Tools for Office (VSTO), when you are loading a VSTO add-in.
First, you need to identify the system properties on your machine.
(Win10) Click Start -> Settings -> About (1) -> Under Related Settings, click System Info (2) -> Advanced System Settings (3) -> Advanced (4) -> Environment Variables... (5)
Add a new system variable and type the following:
Variable name: VSTO_SUPPRESSDISPLAYALERTS
Variable value: 0 (zero)
Clik OK, and restart Office programs.
Within Word you go to Options -> Add-ins -> Com Add-ins -> Go...
Enable the your add-in again, and you should now get errors messages displayed if any are present:
In PowerShell or Command Prompt
It is possible to set the environment variable for the current user with no restart or admin rights required.
To display VSTO errors:
SETX VSTO_SUPPRESSDISPLAYALERTS 0
To not display VSTO errors:
SETX VSTO_SUPPRESSDISPLAYALERTS 1