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 a filesystem without losing one or more files, so it wants to defer this responsibility to you, the administrator. Data corruption has probably already occurred.