There are several conditions which need to be satisified in order to boot from Darwin:
- You need a valid partition map.
- You need a UFS partition.
- That UFS partition needs to be marked active, unless you want to manually select that partition every time you boot. To flag a partition as active, use the "flag" command within fdisk.
- You need to specify that Darwin boot from the UFS partition, as detailed in the Booting section.
Double-check that your installation satisfies all of the above conditions. If you are still having difficulties, consider posting to the discuss mailing list.