When run on a command prompt script runs with local user permission.
The same script when run from a browser runs as user IUSR_<<computer_name>>. This user being a guest account user doesnot have permission to work with processes.
Try giving IUSR account full permissions. This is the scenario with IIS. I hope a similar thing exists with Apache. Give it a try.

****Giving IUSR account, full permissions is not recommended*****

Regards
-Amar