How to mount a FreeBSD-5.1 partition from FreeBSD-4.9

[Juan Rodriguez Hervella]

Hello, please send the reply to myself cause Im not 
subscribe to the list

I've got a FreeBSD-5.1 installation in /dev/ad0s3,
but I usually run FreeBSD-4.9 from /dev/ad0s2.

When I run:

root at cimborrio:/usr/home/jrh# mount /dev/ad0s3 /mnt/freebsd5.1
(ERROR)mount: /dev/ad0s3 on /mnt/freebsd5.1: incorrect super block

root at cimborrio:/usr/home/jrh# mount /dev/ad0s3a /mnt/freebsd5.1
(ERROR)mount: /dev/ad0s3a: No such file or directory

Has anybody else experienced these problems ?
What can I do ?

Thanks in advance!