Once in a whiles, one finds that the non-intuitively obvious wacks
one up side da head, and the aw s!&!t Eureka! finally sets in, and
a solution ensues......(:+}}...  For several weeks, half a dozen of
my ss5/20 pizza boxes had been giving me esp0: invalid state: 6
errors, when running 1.6 and later, and not on 1.4.x or 1.5.x.  It was
becoming rather frustrating, and it seemed to point to cd problems.
Yet, I changed cdroms up the kazoo, and still the error occurred.

Finally, a not-so obvious solution, ensued.....(:+}}...

I noticed that when a machine was hooked up to external drives,
the problem seemed to go away many times.  Yank the external
boxes and add a terminator dongle, and back it came.  Finally,
I got to looking at scsi terminator blocks, and noticed that on the
machines in question, lo and behold, the terminator blocks just
ever so slightly did not fit correctly into their back-panel receptacles.
The Sun receptacles have a bevelled end on each side of the shell.
I was reaching into my box of terminators and just slapping one on.
It turns out that depending upon the manufacturer of the terminator
block, a bevelled or a straight ended shell might be used.  The ones
with the bevelled shell ends fit nicely into the Sun receptacle.  The
ones with the straight ended shells just ever so slightly don't fit
nicely into the Sun receptacle.  Thus, if not fully seated, some of
the terminator blocks may not correctly terminate some scsi bus
lines, and result in the dreaded esp0: invalid state: 6 error, ad nauseum.

(:+}}.... geesh!

I hereby award meself the first Geek Dunce of the Month Award, 
for not carefully checking every last scsi terminator to seat fully
and correctly.....(:+\\.....

As pennitance, I shall herewith thrice read, cover to cover,
Lions' Commentary on 6th Ed.....

Hope you have better luck!

Bob Keys

p.s.  For years I have been using the plastic HD50 ribbon cable with
plastic connectors to make short 6 inch runs between boxes on Sun
stuff.  Religiously, I carefully file and bevel each connector shell so it
fits correctly.... now I will do likewise to each terminator block!