@Matt_H
I read the Deneb manual so I knew that buster 11 had issues with Dma

I tried eliminating everything in the startup-sequence, one by one adding things back in, that's how I worked out that it was the Setpatch command, then I tried Nocache and voila... It's the data cache that causes the problem...
I don't have anything in the wbstartup... The 3000 just boots off an usb flash so apart from the Deneb there is nothing else in there, the 4000 has a Buddah installed...
@Alexh, on the 3000 I just have the poseidon files in the flash rom, in the 4000 nothing at all...
(actually the 4000 now has no motherboard, it's on it's way to Anthony Hoffman for some TLC)