Adding slice on existing disk

[Leslie Jensen]

On a dualboot system I've made some space available that I want to make 
a freebsd slice of.

Following the instructions described here:

http://forums.freebsd.org/showthread.php?t=2726

When using sysinstall label I get this when I try to write.

Error mounting /dev/ad4s4d on /data : File or directory does not exist

I have created
drwxr-xr-x   2 root  wheel         512  1 Mar 09:51 data/

I get the same error and I try to use bsdlabel manually but I get:

bsdlabel -w /dev/ad4s4
bsdlabel: unable to get correct path for /dev/ad4s4: No such file or 
directory

Any suggestions on how to solve this?

Thanks

/Leslie