File created without content with PHP

I have XAMPP installed on a machine with Windows 8 Enterprise . Developing in PHP happens that when loading the page a temporary file is created in the folder C:\Temp having as content a certain IP address.

$tmpfname = tempnam("C:\Temp","CCT_");
$handle = fopen($tmpfname, "w");
fwrite($handle, $circuito['loopback0']);
fclose($handle);

Renaming this temporary file to a default name.

$conn= rename($tmpfname, "C:\Temp\conecta.txt");

It is accessed later where this IP is read and used to make a connection with Telnet .

On my machine this works completely, but when accessing the page from other machines, the file is created with the default name, but without content (blank).

What could be causing this problem?