I've got one Vax (Vaxstation 3500) that I've not been able to netboot,
getting the 4B CTRLERR.  However, by disconnecting and reconnecting
the tape drive, I've been able to get the machine to start booting from
tape.  However, I haven't seen much written about the procedure, aside
from the FAQ, which is out of date.

I made the boot tape on a Pmax, using:

mt -f /dev/rmt0 rewind
dd if=miniroot.fs of=/dev/rmt0
mt -f /dev/rmt0 rewoffl

Then I stuck the boot tape in the drive, and did:

B/3 MUA0

I get the first bootloader prompt, which still gets stuck at 5 in the 
countdown, but here I get enter, and I'm dropped into the '>' prompt.
Here I try "boot" or "boot netbsd", and in either case, I get the 
message "no such file", after the tape drive spends some time 
looking about on the tape.  Am I following the proper procedure, 
or should I being doing something else?

Doug