I figured out my problem. My /etc/fstab originally had the following entry: (I made a mistake, setting the mount point to / instead of /datastore).
/dev/VolGroup01/LogVol00 / ext3 defaults 1 1
The kernels were installed while this incorrect entry existed.
I then manually modified the /etc/fstab again with the correct entry (as in my original post):
/dev/VolGroup01/LogVol00 /datastore ext3 defaults 1 1
Rebooted, but still had the problems. I couldn't figure out how to manually re-run the POSTINSTALL SCRIPTLET for the kernels, so I just removed them with yum, and re-installed only the latest kernel, which in turn re-runs the postinstall script and on reboot, everything is OK.
However, can someone point me to a good article on re-running the postinstall scriptlet. One that has some good examples and such... Thanks.