ZFS and Jails (dataset does not exist)

Hi,

i am trying to setup a jail within ZFS.
What i did:

#zfs create zeta/jail
#zfs set jailed=on zeta/jail

Ok.

#zfs jail 1 zeta/jail
WARNING pid 819 (zfs): ioctl sign-extension ioctl ffffffffcef85a2b
cannot jail 'zeta/jail': dataset does not exist

Now i am stuck here.

base.?? should bei extracted to zeta/jail?

Thanks in advance.

Axel