RHEL 4.0 WS unix_chkpwd question

[Blackburn, Marvin]

Since upgrading to the latest kernel and erratta,
I have been getting the following when logging in to system xxxxx as
user yyyy.
I have seLinux in a monitoring mode.  
What has caused this and what about the password is this checking?

Dec 21 10:35:38 xxxxx unix_chkpwd[17107]: password check failed for user
yyyyy

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Marvin Blackburn
Systems Administrator
Glen Raven
"He's no failure.  He's not dead yet" --William Lloyd George