adding Locale in Solaris 10 - en_US.UTF-8

I have the solaris ISO mounted for remote install and can see the contents fine When I try to do the following to add en_US.UTF-8:
localeadm -a en_US.UTF-8 -d /mnt

I get the following messages:
Log file is /var/sadm/install/logs/localeadmin_install.2011-05-11.1

locale/region name is en_us

Warning! You have chosen the en_US.UTF-8 locale rather than a region to install.
This locale is part of the North America region. If you choose to continue, all of the locales in this region will be installed.

Do you wish to continue? [y/n]: y
Adding packages for North America (nam)

Region nam is already installed on this machine. Exiting


When I check the locales I get : (note no en_US.UTF-8 shown)
-bash-3.00# locale -a
C
POSIX
en_CA
en_CA.ISO8859-1
en_CA.UTF-8
en_US
en_US.ISO8859-1
en_US.ISO8859-15
en_US.ISO8859-15@euro
es
es_MX
es_MX.ISO8859-1
es_MX.UTF-8
fr
fr_CA
fr_CA.ISO8859-1
fr_CA.UTF-8
iso_8859_1