Executing Python script for GRASS from PHP

I wrote the following Python script:

#!/usr/bin/env python
import os
import sys

gisbase = os.environ['GISBASE'] = "/usr/lib/grass64"
gisdbase=os.path.join("PATH")
location=LOCATION NAME
mapset=MAPSETNAME
sys.path.append(os.path.join(os.environ['GISBASE'], "etc", "python"))

import grass.script as grass
import grass.script.setup as gsetup
import grass.script as grass
 
gsetup.init(gisbase, gisdbase, location, mapset)
print "one"

grass.run_command('v.in.ascii','-o', input='/opt/lampp/htdocs/project/basic_statistics/sites_grass.csv', output='sites',fs=",",skip='1', x='9', y='10')
print "two"

grass.run_command('v.db.addcol', map='sites', columns="height INTEGER")
grass.run_command('g.region', rast="dem21")
grass.run_command('v.what.rast',vector='sites', raster='dem21', column='height')
print "three"

grass.run_command('v.out.ascii','-o', input="sites",output="sites_geography_stats.csv", columns='height')
print "four"

It runs without any problems when I simply execute it from UNIX terminal (/.FILENAME.py). However, my goal is to execute it from a PHP code:

<?php
...
echo system("./FILENAME.py");
...
?>

When I run the PHP code the following output is printed to the website:
one two three four

Sadly, the sites_geography_stats.csv file is not created. It looks that the python script is executed from php but its GRASS-related part is ignored.
Does anybody have any ideas how to fix it?