Existing lock /var/run/yum.pid: another copy is running as pid 523.

I'm running the command yum update -y and getting the following error:

Loaded plugins: fastestmirror, priorities
Existing lock /var/run/yum.pid: another copy is running as pid 523.
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 - 14 day(s) 11:47:39 ago
State : Sleeping, pid: 523
Another app is currently holding the yum lock; waiting for it to exit...
The other application is: yum-updatesd-he
Memory : 14 M RSS ( 26 MB VSZ)
Started: Tue Feb 9 08:19:02 2010 - 14 day(s) 11:47:41 ago
State : Sleeping, pid: 523

How do I fix this problem?

Run the following command to find out process associated with yum command:
# ps aux | grep -i yum
Sample outputs:

root       523  0.0  0.7  27128 14624 ?        SN   Feb09   0:00 /usr/bin/python -tt /usr/libexec/yum-updatesd-helper --check --email --email-from=vivek@nixcraft.net.in --email-to=vivek@nixcraft.net.in --smtp-server=localhost:25 --sendmail
root      2875  0.0  0.5  26456 10620 ?        SN   Jan23   0:00 /usr/bin/python -tt /usr/sbin/yum-updatesd
root     25840  0.0  0.6  24224 12800 ?        Ss   11:58   0:14 /usr/bin/python /usr/bin/yum update -y
root     26665  0.1  0.6  24228 12784 ?        Ss   20:02   0:00 /usr/bin/python /usr/bin/yum update -y
root     26785  0.0  0.0   4128   608 pts/0    S+   20:06   0:00 grep yum

Kill PID 523, 25840, and 26665:
# kill -9 523
# killall -9 yum
Now run the following:
# yum update -y
Make sure you start yum-updatesd:
# /etc/init.d/yum-updatesd start