yum update pam problems

[Margaret Doll]

I have many Redhat and Fedora systems.  Two of the systems are having  
problems updating pam

One is running 2.6.18-128.1.14.el5.  The other is running   
2.6.18-128.1.6.el5xen


When I issue:

yum update pam

it ends in

Metadata file does not match checksum
  You could try using --skip-broken to work around the problem
  You could try running: package-cleanup --problems
                         package-cleanup --dupes
                         rpm -Va --nofiles --nodigest

I followed all the suggestions and even issued

rpm --rebuilddb

These steps did not help.