unable to mount swap backed device

[Mipam]

Hi,

I've been trying to mount a swap backed mfs, but it seems inpossible.
On questions i've gotten no answer. Thing is, i am able to mount the stuff
in 4-stable, but not in 5.2.1-p4.
I added the line:

/dev/amrd0s1b   /var/amavis   mfs   rw,-s=65536   0   0

to /etc/fstab
but i cant mount /var/amavis, in 4-stable it works fine.
I have

device            md              # Memory "disks"
in the kernel config so i dont see why it doesnt work.
Can anybody give any hints what's going on?
When i try it manually i get:

mount_mfs: bad device unit: amrd0s1b
Bye,

Reinoud.