Weird fdisk behavior

[Baldur Gislason]

I am trying to add another partition to my root drive, it has a few gigabytes of unpartitioned space.
Whenever I try to run fdisk -u it says cannot open disk /dev/ad0: No such file or directory
ad0 does exist, why does fdisk say otherwise? fdisk can display the partition table but it can't alter it.
securelevel is -1 and this is FreeBSD 5.4-STABLE from the beginning of May this year.

Baldur