This is almost certainly a 'permissions problem' That is, the userid under which your http server (IIS; Apache or whatever) runs, does not have the authority to execute the netsh command, whereas your own userid (when you run it on the command line) does.

The 'fix' would be to give the user id your web server runs under the required priviledges; but you should seriously consider whether you want to do that, given the potentially substantial risks involved in allowing anyone who access your webserver, the power to mess with your system to the extent that the netsh command gives them the power to do.

Do not underestimate the risks involved. If you have any doubts about your ability to a) control who has access to the webserver; or b) whether there is anyone who could access it that might use that access to do things that you don't want them to do; reconsider!