I am getting some kind of "unknown block" or something
similar when
trying to boot up with this kernel, whereas with .14 it boots up fine.
You've most likely upgraded mkinitrd to 3.5.16.1-1 before installing
2.6.0-1.21. You might want to take a look at bug #112623,
<
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=112623>. In any
case downgrading mkinitrd to a previous release, say, 3.5.14-1 or
3.5.15.1-2 and re-installing kernel 2.6.0-1.21 should resolve your
problem.
Next time you might want to add a bit more detail to your problem
description ;-)
// kaj