I have had a recurring problem on my PC for a while where after some period of time Visual Studio will fail to start and show a generic error message box. I have multiple versions of Visual Studio and all would fail to load, none telling me exactly what the problem was. I experienced a similar problem trying to start SQL Server Management Studio. Every time this happened, the only thing that could fix it was a reboot. I had tried a few times to search online for similar problems with Visual Studio, but could find nothing useful. Not knowing where to start in troubleshooting, I settled with rebooting occasionally.

Recently when this problem occurred, I happened to try to start Paint.Net as well, and it also failed to load. It, however, give me a much better error with a call stack. It reported a TypeInitializationException coming from the Microsoft internal static class FontCache.Util. The inner exception indicated a UriFormatException. Using Microsoft’s wonderful code reference site, I pulled up the code for FontCache.Util and examined the constructor. In doing so, I found that the code does indeed try to create a Uri based on some string value built using environment variables.

I started up a fresh instance of LinqPad and pasted the code from the Microsoft site and ran it to see what happens. Sure enough, I experienced the same exception. I inspected a few variables and found that the environment varible “WinDir” was coming back as null. Finally something to start researching. I ended up finding this Superuser question about environment variables that stop working after a while and seemed to have put together the final piece of the puzzle. According to the posted answer, having a very long PATH variable can cause the WinDir variable to fail. I did have a long PATH, so I deleted a bunch of things that didn’t seem necessary and my problem was resolved! Thank goodness for Paint.Net showing the real error I would have never known where to start.

I hope that writing this post will help someone else searching the internet trying to find out why Visual Studio is not starting. I couldn’t make the connection online, but hopefully this post can help fix that.