Sysinstall & labels/fdisk

Hi

I have run in to an odd problem that on a freebsd 5.2 current system after
running fdisk and disklabel the initial time on install, i am never allowed
to do it again. 

What I have tried on many different systems, is to run sysinstall, and
either run fdisk or label. After making a change and trying to write the
changes, it will fail. Even if you dont make a change, and just try to write
the current settings to the disk, it will fail. The following error comes up
"ERROR: Unable to write data to disk ad0" (if also tried different types of
disk devices - da/aacd). Ktrace shows the error as "errno 1 Operation not
permitted"

Anyone have any ideas or input?
Thanks