I recently tried to install NDepend (http://www.ndepend.com/) version 6 to my home machine.
Visual Studio Extension Installer for Visual Studio 2013 worked just fine.
Visual Studio Extension Installer for Visual Studio 2015 failed with an error caused by a mis-configuration of my machine shown below.
Can’t install NDepend Visual Studio 2015 extension.
Reason: Can’t run VSlXlnstaller.exe to install NDepend Visual Studio
Reason: Can’t find the path to the file VSlXlnstaller.exe
Reason: Can’t resolve the environment variable %VS140COMNTOOLS% to an existing path.
I examined my environment variables (by issuing the SET command from a DOS prompt) and noticed that my VS140COMNTOOLS pointed to a path on the R drive that no longer existed. This was a side-effect of having previously installed Visual Studio 2015 Enterprise RC on the “R” drive, uninstalling it, and re-installing it on the “C” drive. Apparently the reinstallation did not replace or update the environment variable. Once I corrected the path (using System, Advanced, Environment Variables) to point to the valid location, C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE, I had no trouble installing the Visual Studio Extension for 2015. This is an odd situation, and I only include it here in case someone else has uninstalled and re-installed their Visual Studio to another drive at some point. Perhaps searching for this error will help.