I have had this same problem when executing a build script in a cmd window. After about 13 times I got that same error. The build script had to make sure that vcvarsall.bat was run so it executed vcvarsall.bat every time.
vcvarsall.bat is not smart enough to only add things to the path if they are not already there so a bunch of duplicate entries were added.
My solution was to add an if defined check on an environment variable which I know is set by vcvarsall.bat…
if not defined DevEnvDir (
call vcvarsall.bat
)
Check your path environment variable after each run and see if it is growing. If it is and there are duplicates, you will need to be smart about adding stuff to the path. There are several ways to be smart about it.