FreeBSD's boot loader is incorrectly recognizing the hard drive's geometry. This must be manually set within fdisk when creating or modifying FreeBSD's slice.
The correct drive geometry values can be found within the machine's BIOS. Look for the number of cylinders, heads and sectors for the particular drive.
Within sysinstall(8)'s fdisk, hit G to set the drive geometry.
A dialog will pop up requesting the number of cylinders, heads and sectors. Type the numbers found from the BIOS separates by forward slashes.
5000 cylinders, 250 sectors and 60 sectors would be entered as 5000/250/60
Press enter to set the values, and hit W to write the new partition table to the drive.