Visual Studio 2017 Extension Load Error

After installing quite a few extensions by using the Extensions and Updates command on the Tools menu, I started to get a load error every time I opened Visual Studio, telling me to check the ActivityLog.xml in the C:\Users\…\AppData\Roaming\Microsoft\VisualStudio\15.0_709865ab folder. I opened the file and found numerous entries like this one:

System.ComponentModel.Composition.ImportCardinalityMismatchException: Duplicate EditorFormatDefinition exports with identical name attributes exist. Duplicate name is PowerShell Interactive – Black

I suggested to me I had to check for duplicate extensions, and I had indeed installed two editions of the same extension, PowerShell Tools for Visual Studio 2017 as well as the old one, PowerShell Tools for Visual Studio 2015. Uninstalling the latter solved the issue. 🙂