I have a 486/33 with an adaptec 1522 SCSI controller (aic driver) and
some old crufty drives [1] hooked to it.  occationally during heavy disk
activity, I get four 'sd0: not queued, error 5' messages on the console,
and then the machine wedges.

according to the thread "sdX: not queued, error 5" at
http://mail-index.netbsd.org/tech-kern/1997/03/ the ahc driver had the
same problem, and it looks like Jason had a fix for it.  Would the same
approach work for the aic driver?  (the activity LED doesn't light,
either... maybe that could be fixed, too.)

[1] five 100MB RZ23s and a geriatric 40MB seagate

-- 
  Aaron J. Grier | "Not your ordinary poofy goof." | agrier@poofygoof.com