I am not an expert... The workaround just worked, but I don't know whether "00000692 Marvell RD-88F6281 Reference Board" is a valid machid for the sheevaplug, instead of the 'original' 00000831.
At the beggining it worked, but now I have a problem: the sheevaplug ethernet subsystem does not work well... It does not get an IP by DHCP and assigning a static one does not work either... I suspect that is caused by the workaround but I don't know. So I do not recommend doing the procedure/workaround of changing machid, as it may be unsafe and I warn thay may damage the hardware. I hope Martin's solution will work... Where will you post the kernel image?