How can I make this counter work in Plesk?

[Clark]

This is a simple script I used previously on a server running with Cpanel. I have not been able to make it work yet under Plesk.

I have the count.php file located in a directory of my site like
mysite.com/forum/count/count.php

It takes the message numbers, checks if a file name of that number exists in the count directory and writes and increments the counter for each file.

It is called as an include from a message located on my site at an address like mysite.com/forum/messages/12345.php

Here is the counter code. The test $number I am passing to the counter is 777.

<?
if (file_exists("$number")) {
        $fd = fopen("$number", "r"); 
        $num =  fread($fd, filesize("$number")); 
        fclose($fd);
}
else {
        $fd = fopen("$number", "w+"); 
        $num = "0"; 
        fclose($fd);
}

        $fd = fopen("$number", "w"); 
        $read = $num + 1; 
        echo "$read"; 
        fwrite($fd, $read); 
        fclose($fd); 
?>

Here are the error messages I receive:

PHP Warning:  fopen(777): failed to open stream: Permission denied in /home/httpd/vhosts/mysite/httpdocs/forum/count/count.php on line 12

PHP Warning:  fclose(): supplied argument is not a valid stream resource in /home/httpd/vhosts/mysite/httpdocs/forum/count/count.php on line 14

PHP Warning:  fopen(777): failed to open stream: Permission denied in /home/httpd/vhosts/mysite/httpdocs/forum/count/count.php on line 17

PHP Warning:  fwrite(): supplied argument is not a valid stream resource in /home/httpd/vhosts/mysite/httpdocs/forum/count/count.php on line 20

PHP Warning:  fclose(): supplied argument is not a valid stream resource in /home/httpd/vhosts/mysite/httpdocs/forum/count/count.php on line 21