Solaris lucreate ERROR: Unable to mount boot environment

# /usr/sbin/luupgrade -u -n NEWBE -s /mnt -k /tmp/sysidcfg

64459 blocks
miniroot filesystem is 
Mounting miniroot at 
ERROR: Unable to mount boot environment <>.

Live Upgrade uses /a as a temporary mount point and directory for some of its actions.
Check /a to make sure it is empty in the current BE and the new BE.

# cd /a
# ls
file1
# rm file1
# /
# lumount NEWBE /mnt
# cd /mnt/a
# ls
file1
# rm file1
# cd /
# luumount NEWBE 

After that try again. You can also delete your NEWBE , recreate it. Clean up /a and try agian.