[CentOS] LVM Snapshot Create Error

Just discovered that on CentOS 4.1 when you issue the command:

	lvcreate -s -n temp -L2G /dev/vgname/lvname

to create a snapshot, you get the error message:

	snapshot: Required device-mapper target(s) not detected in your kernel

I've checked and recheck my spelling and tried using the device created
under /dev/mapper. I've tried it on both x86_64 and on i386. Works as
expected under CentOS 3.5.

Any ideas what is going on?