Boot process question:

At line 446 in mbr.S, error "No opearting system".  According to mbr(8):

      3 No operating system     The bootsector was loaded successfully,
                                but it was not valid (i.e., the magic num
                                ber check failed, or it contained no
                                code).


To expound on this, the MBR code was able to:

1) find and select active partition, but...
2) but unable to read the boot block in the first sector?

"boot block" referering to /usr/mdec/bootxx_* installed into first slice?

Possible causes would be an invalid partition table?

Thanks,
~BAS