Cause

At boot time the /etc/rcS script runs the fsck(1M) command to check the integrity of filesystems marked "fsck" in /etc/vfstab. If fsck(1M) cannot repair a filesystem automatically, it interrupts the boot procedure and produces this message. When fsck(1M) gets into this state, it cannot repair filesystems without losing one or more files, so it wants to defer this responsibility to you, the administrator. Data corruption has probably already occurred.