Cause: You still have the old FreeBSD 1.x boot blocks on your boot partition.
Solution: You should re-enter the installation process, invoke the (F)disk editor and chose the (W)rite option. This won't hurt an existing installation and will make sure that the new boot blocks get written to the drive. If you're installing for the first time, don't forget to (W)rite out your new boot blocks! :-)