During an audit, we noticed that one of our Red Hat 5 / CentOS 5 servers wasn’t getting the security patches.  Upon running the yum update command manually, we discovered that it fails with:

Error: kernel conflicts with e2fsprogs < 1.37-4

The problem turned out to be the presence of a number if 32bit packages. To solve it, we removed the 32bit architecture packages with:

yum remove *.{i386,i586,i686}

(only do that if you are on x86_64 and you verified that the packages you need are present in 64bit version)