fdisk - can't update an in-use partition

[João Pinheiro]

Hi,
I have freebsd 6.2 installed on a disk with a 260Gb partition with only 
a 30Gb label (don't ask :P) and I'm trying to resize the active 
partition to the size of the existing label, so I can create another 
partition. I've already set kern.geom.debugflags=16 to be able to write 
to mbr, but fdisk doesn't update my disk and gives the following error:

fdisk: conflict with open slices

Does anywone know a way to force fdisk to update the partition table? 
This is a remote machine so I can't boot from CD to correct the 
partition table and/or reinstall the SO.

Thanks in advance,
    João Pinheiro