Algumas funções do Php precisam ser desabilitadas em servidores web compartilhados. Altere os mesmos em:
/usr/lib/php.ini
Se o Zend foi compilado, o caminho pode ser:
/usr/local/Zend/etc/php.ini
Lozalize a linha: disable_functions = e digite as funções:
xec, system, passthru, shell_exec, escapeshellarg, escapeshellcmd, proc_close, proc_open, dl, popen
Ou, mais completo:
dl, system, exec, shell_exec, chown, chgrp, escapeshellcmd, putenv, popen, pclose, passthru, proc_open, proc_get_status, proc_nice, proc_close, proc_terminate, posix_ctermid, posix_get_last_error, posix_getcwd, posix_getegid, posix_geteuid, posix_getgid, posix_getgrgid, posix_getgrnam, posix_getgroups, posix_getlogin, posix_getpgid, posix_getpgrp, posix_getpid, posix_getppid, posix_getpwnam, posix_getpwuid, posix_getrlimit, posix_getsid, posix_getuid, posix_isatty, posix_kill, posix_mkfifo, posix_setegid, posix_seteuid, posix_setgid, posix_setpgid, posix_setsid, posix_setuid, posix_strerror, posix_times, posix_ttyname, posix_uname
FONTE: http://www.forumcpanel.com.br/index.php?showtopic=368&pid=2002&mode=threaded&start=#entry2002