500 OOPS child died
 

I use Fedora Core 7 , try to setup vsftp.Here is my vsftp.conf file ,
anonymous_enable=YES
local_enable=YES
write_enable=YES
local_umask=022
#
#anon_upload_enable=YES
#anon_mkdir_write_enable=YES
#dirmessage_enable=YES
#
xferlog_enable=YES
connect_from_port_20=YES
#
#chown_uploads=YES
#chown_username=whoever
#
xferlog_file=/var/log/vsftpd.log
xferlog_std_format=YES
idle_session_timeout=600
data_connection_timeout=120
nopriv_user=nobody
#
#async_abor_enable=YES
# ASCII mangling is a horrible feature of the protocol.
#ascii_upload_enable=YES
#ascii_download_enable=YES
#ftpd_banner=Welcome to blah FTP service.
#deny_email_enable=YES
# (default follows)
#banned_email_file=/etc/vsftpd/banned_emails
#chroot_list_enable=YES
# (default follows)
#chroot_list_file=/etc/vsftpd/chroot_list
#
ls_recurse_enable=YES
listen=YES
pam_service_name=vsftpd
userlist_enable=YES
#
#tcp_wrappers=YES
#


I got this error when i try to login via ftp client.
Does anybody know how can i solve this.

Thanks a lot