Launching an application: Does PHP limit network connections?

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Hi folks,

I am having a problem using PHP to launch an application on the server.  
All the basics work, but I cannot launch more than 4 instances of the  
application. This application functions as a server itself, and I  
specify the port number when I launch it, so my theory is that I am  
reaching some limit on network connections.

This is my basic launch sequence:

$command = 'c:\Program Files (x86)\myprog\myprogram.exe';
$arguments = ' /Port:' . $port;
exec('C:\PsTools\psexec.exe -accepteula -d -s "' . $command . '" ' .  
$arguments . ' 2>&1', $output);

Note that I am using psexec because I need to keep track of the process  
ID number and kill the application when a user logs out. I can provide  
more details if needed, but if there is indeed some upper limit on port  
connections, that would certainly explain what I'm seeing.

Incidentally, if I try this same procedure launching "Internet  
Explorer", my limit is 9 (instead of 4). If I launch a non-network  
application, it seems that I can launch as many as I want without limit.

Note: I am using Windows XP Professional x64 Edition SP1

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