I too am unable to install the Pmax netbsd port on an Ultrix workstation 
(DECstation 2100) with two scsi disks.  The disklabel goes fine, no
complaints anywhere, install the bootblocks, copy the miniroot,
and get an error 11 when trying boot -f rz(0,2,0)netbsd.

I followed Arne's instructions, including the "swapped" a partition.

Earlier, I tried following the Installation guide on the WWW site, but
that is obviously completely out of date.  I got an error 25 when
trying that.

Any suggestions?