One very useful trick to debug VSTO applications is this “cheeky” flag: VSTO_SUPPRESSDISPLAYALERTS. It’s a environment variable to enable error messages about dodgy exceptions, like COM exceptions. For example, I was getting a strange behavior in my Office Word application when I was trying to add a new Plain Text Control:
However, my VSTO application didn’t show me any messages or warning about any error, until I added this environment variable VSTO_SUPPRESSDISPLAYALERTS to my system with value 0. Next, I got this message:
It means that you can’t set a Plain Text Control title bigger than 64 characters.
Don’t forget this friendly helper 🙂