come faccio a gestire il chmode di un file .php

Praticamente ho un file di che visualizza gli utenti online

formato da 2 file 1. online.php e 2. data.php(è un file praticamente vuoto)

mi genera questo errore

Warning: fopen(data.php) [function.fopen]: failed to open stream: Permission denied in D:\Inetpub\webs\automobilicorsinoit\online.php on line 10

file n. 1 online.php

<?
$timemax = "200"; //Max. tempo utenti on line sul sito
$ipadress = $REMOTE_ADDR;
$timenow = explode (" ", microtime());
$timenow = $timenow[1];
include ("data.php");
$timedelete = $timemax;
$deleted = $deleted + $timedelete;
if ($deleted < $timenow){
$file = fopen("data.php","w+");
fputs($file, "<?PHP \$deleted = \"$timenow\"; ?>\n");
$number = count($visitor_b);
for ($tel = 0; $tel < $number; $tel++){
$visitor_a = $visitor_b[$tel];
$visitor_a[0] = $visitor_a[0] + $timemax;
if ($visitor_a[0] > $timenow)
fputs($file, "<?PHP \$visitor_b[] = array('$visitor_a[0]','$visitor_a[1]'); ?>\n");
}
fclose($file);
}
$visitor_b = "";
include ("data.php");
$number = count($visitor_b);
for ($tel = 0; $tel < $number; $tel++){
$visitor_a = $visitor_b[$tel];
if ($visitor_a[1] == $ipadress)
$save = "nee";
}
if (!$save){
$file = fopen("data.php","a");

fputs($file, "<?PHP \$visitor_b[] = array('$timenow','$ipadress'); ?>\n");
fclose($file);
}
$visitor_b = "";
include ("data.php");
$number = count($visitor_b);
for ($tel = 0; $tel < $number; $tel++){
$visitor_a = $visitor_b[$tel];
$visitor_a[0] = $visitor_a[0] + $timemax;
if ($visitor_a[0] > $timenow)
$online = $online + 1;
}
if (!$online)
$online = 1;
if ($online == 1)
echo "<font color='#FF0000'>".$online."</font> utente online";
else
echo $online." utenti online";
?>