i found that on the web, may be an explanation:
Sometimes if the bootlv is outside the first 4gb of disk this can
happen. It's worth a try to do the following:
Boot into maintenance mode, mount the filesystems and type the
following:
# rmlv hd5
# mklv -t boot -y hd5 -a e rootvg 1 hdisk0
# bosboot -ad /dev/hdisk0
Then reboot.