writing to text file

[Pouncer]

i uploaded a text file called 'logs.txt' and write.php to a www folder on a server (i got a subdomain)

so the links to these are like, E.G:.
www.site-here.com/logs.txt
www.site-here.com/write.php


then why doesnt something like this work:

www.site-here.com/write.php?txt=Hello

and it should write the word 'Hello' to logs.txt

Heres write.php..

<?php
$filename = 'logs.txt';
$somecontent = $_GET['txt'] . "\n"; 

if (is_writable($filename)) {

   if (!$handle = fopen($filename, 'a')) {
         echo "Cannot open file ($filename)";
         exit;
   }

   if (fwrite($handle, $somecontent) === FALSE) {
       echo "Cannot write to file ($filename)";
       exit;
   }
   
   echo "Success, wrote ($somecontent) to file ($filename)";
   
   fclose($handle);

} else {
   echo "The file $filename is not writable";
}
?>

any help guys?

i just keep getting: Cannot write to file logs.txt