scripts never fork: Unable to fork

Hi! I am having this issue on my Apache 2.2.13 webserver running PHP 5.2.3 on a Kernel 2.6.30.4 Linux Box. error_log: [Sat Mar 20 23:41:34 2010] [error] [client 127.0.0.1] PHP Warning: exec() [<a href='function.exec'>function.exec</a>]: Unable to fork [cat /proc/loadavg] in /server/apache/htdocs/test.php on line 3 The code of test.php is <?php echo exec( 'cat /proc/loadavg' ); ?> Replacing the exec() for system() or shell_exec() or any other program execution function is not working. Running the command line $ php test.php as the apache user works fine. All usual php pages (foruns, phpmysqladmin, phpinfo, etc) works great, except for the fork functions. Ideas and help are welcome, Thank you! Eduardo Nunes