This may or may not help, but I've been fighting a boot lockup and USB dropouts on my A3K ever since I got my DENEB a few years ago.  Those errors are very familiar to me.

I finally resolved the lockup and errors this week by removing the PsdStackloader line from the User-Startup; this was saved in the ROM of the DENEB as well so I wondered why it was running from both places and took a chance.  It paid off.  Since I removed the line, I haven't had a single boot lockup.  I'm thinking there is something that gets confused when this command tries to re-do what was done from the ROM call.

The only downside now is that when I warm boot, I lose my USB network dongle.  I guess I now know why it was in both the ROM and User-Startup now.  But a power cycle to it in Trident brings it back and to me that's a lot easier to live with than a boot lockup that happens 9 out of 10 times.

I'm going to try to fiddle with the PsdStackloader in User-startup when I get time to see if I can correct the locks without having to remove the line for good but at least I'm in a better place now.

I don't know if the ROM on the Rapidroad has the PsdStackloader in it but maybe you'll get lucky and this is the trick you're looking for...

Getting back to Dan Wood's problem, it seems that you have a hardware problem that I had happen with a partially bad Buster 11.  Replacing it my X-Surf 100 and RapidRoad worked fine.  I also had the MB recapped, but I don't believe that cleared any issues but weak audio in one channel.

Kernel, the wrong programs in Deneb ROM have caused me issues as well.

Did you try cleaning the Zorro slots and reseating the Buster?

Confirmed by Jens on EAB it's a A3640 problem.

http://eab.abime.net/showpost.php?p=988633&postcount=210

Downgraded to Zorro 2 mode and works fine.  Hoping for a bug fix so I can run my Ethernet back in Z3 mode!

I cleaned the Zorros thoroughly last month, and replaced my Buster 9 with a new 11 from Amigakit a few weeks ago.  Everything else on the system seems to be working flawlessly, the X-Surf, Picasso IV, Bigram +

I've had some suggestions that it could be a PSU issue as the A4000 PSU might be pushed to its limit with an RTG Card, RAM and the X-Surf.

I don't have the Rapidroad connected to the floppy power though, is that mandatory?  The included instructions suggested it was just optional for high powered USB devices.  I have ordered a molex to floppy adapter so I can plug it in though.

The a4000 psu should power all that without breaking a sweat,assuming its in good shape and such. check voltages while it is loaded with everything in use. voltage is not the whole story but its a starting point.

doh, i didn't read far enough,i see the problems solved.