Both global zones and non-global zones contain BEs. Each BE in a non-global zone is associated with a parent BE in the global zone. If a global zone BE is inactive, the related non-global zone BE is unbootable. The unbootable BE is flagged with ! when you display a list of BEs. Booting into the parent BE in the global zone causes the related non-global BE to become bootable.
Note that if a BE becomes unbootable, then no other action can be performed on it by any beadm subcommands.