fdisk/bsdlabel: cannot write to disk

[Norbert Koch]

Hello.

I am rather new to FBSD5.3.
I did a custom install leaving
some room on my (ata) hard disks. Later I
decided to create a separate /usr/obj
partition. I started /stand/sysinstall
and tried to create a new slice and
a new partition in it. Sysinstall reported
that it cannot write to the hard disk.
Next I only tried to create a new
partition inside an existing slice.
The same again. I tried the same manually
with fdisk/bsdlabel and the same happens.
I tried it in single user mode and even booted
FREESBIE. Always the same problem.

I must be doing something simple very wrong.
But what? What f*cking manual did I not read?
Is there some secret geom rdonly switch I
have to turn off? (BTW: securelevel is at -1)

Thank you,
Norbert