(Elevated prompt under Windows 7)
(The variable is removed the first time, but gives an error message.)
Code:
129G C:\Users\johnb# set /s foo=foo
129G C:\Users\johnb# unset /s foo
TCC: (Sys) The system cannot find the file specified.
129G C:\Users\johnb# unset /s foo
TCC: Not in environment "foo"
129G C:\Users\johnb# ver
TCC 12.00.41 Windows 7 [Version 6.1.7600]