yum update xxx & firefox fail with segmentation fault on Linux RHES 4.x

My RHES 4.2 box could reach the clam site (ie firewall permitted correctly) :
# telnet www.clamav.net 80
Trying 194.109.142.194...
Connected to www.clamav.net (194.109.142.194).
Escape character is '^]'.

Whenever I tried  "yum update clam" run from root, it wud give  
"segmentation fault" - I've tried restarting clamd (/etc/init.d/clamd restart)
& repeat the update but still getting the same error:

# yum list clamav
Setting up repositories
Segmentation fault
[root@clamav]# yum update clamav
Setting up Update Process
Setting up repositories
Segmentation fault
[root@clamav]# rpm -qa | grep clam
clamav-milter-0.96.1-1.el4.rf
clamav-db-0.96.1-1.el4.rf
clamav-0.96.1-1.el4.rf
clamd-0.96.1-1.el4.rf
#

# /etc/init.d/clamd restart
Stopping Clam AntiVirus Daemon:                            [  OK  ]
Starting Clam AntiVirus Daemon:                            [  OK  ]


From /var/log/messages, I got the following :

Feb  9 16:25:02 hostname dbus: Can't send to audit system: USER_AVC pid=2948 uid=81 loginuid=-1 message=avc:  denied  { send_msg } for  scontext=user_u:system_r:unconfined_t tcontext=user_u:system_r:initrc_t tclass=dbus
[root@hostname log]# vi messages
Feb  6 04:45:01 hostname crond(pam_unix)[30869]: session opened for user root by (uid=0)
Feb  6 04:45:01 hostname freshclam[30874]: ClamAV update process started at Sun Feb  6 04:45:01 2011
Feb  6 04:45:01 hostname freshclam[30874]: Reading CVD header (main.cvd):
Feb  6 04:45:01 hostname crond(pam_unix)[30868]: session closed for user root
Feb  6 04:45:01 hostname freshclam[30874]: Can't get information about db.sg.clamav.net: Name or service not known
Feb  6 04:45:01 hostname freshclam[30874]: Can't read main.cvd header from db.sg.clamav.net (IP: )
Feb  6 04:45:01 hostname freshclam[30874]: Trying again in 5 secs...
Feb  6 04:45:06 hostname dbus: Can't send to audit system: USER_AVC pid=2948 uid=81 loginuid=-1 message=avc:  denied  { send_msg } for  scontext=user_u:system_r:unconfined_t tcontext=user_u:system_r:initrc_t tclass=dbus
Feb  6 04:45:06 hostname freshclam[30874]: ClamAV update process started at Sun Feb  6 04:45:06 2011
Feb  6 04:45:06 hostname freshclam[30874]: Reading CVD header (main.cvd):
Feb  6 04:45:06 hostname freshclam[30874]: Can't get information about db.sg.clamav.net: Name or service not known
Feb  6 04:45:06 hostname freshclam[30874]: Can't read main.cvd header from db.sg.clamav.net (IP: )
Feb  6 04:45:06 hostname freshclam[30874]: Trying again in 5 secs...
Feb  6 04:45:11 hostname dbus: Can't send to audit system: USER_AVC pid=2948 uid=81 loginuid=-1 message=avc:  denied  { send_msg } for  scontext=user_u:system_r:unconfined_t tcontext=user_u:system_r:initrc_t tclass=dbus


I've used "rpm -e yum... " to uninstall, download a fresh copy of yum rpm package
& reinstall  (ie "rpm -i ./yumXXX.rpm ) : the reinstallation completed without error.

However, when "yum update clamav" is run again, it still gave "segmentation fault".

i've also tried to launch firefox browser & it can't launch too (giving segmentation fault
too) : previously firefox could launch.  However Konqueror browser could launch fine.

What's the segmentation fault about ?  Why is it I could launch firefox browser
previously but not this time?

"free -m" showed there's sufficient memory.


Let me know any further information needed