VSTO shows “Unknown Publisher”, Why? How do I fix it?

Unknown Pub

I hope this has not happened to you but if you’re here then you are probably experiencing this problem.

Here where I work this problem became part of my responsibility when our SCM left. Of course I knew nothing about Office Tools or installers. so it was time for a crash course and Google helped some but I could not find info that really helped.

Eventually I did get the info I needed but at first did not know HOW to find this info.

So this is what I learned.

The “Unknown Publisher” was caused because the build server and client machine did not have the latest version of VSTO, Visual Studio Tools for Office.

Sounds easy enough, right? Well, I found that if the user does not have VSTO we will get the correct version. But, if there is a version already there the installer doesn’t care, thus giving the bad publisher message.

How do you get the latest version to install if they already have VSTO? Back to Google and I found this article:


Thank you so much for this simple article that has cleared up my headache for the last few days.

All you have to do is change a simple xml file to set the version number you want of VSTO.

I really hope this article will help others and save you lots of time.