Cause

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