It is maybe not related, but which monitor do you use?
I have a A4000 recapped and Mediator board V3. Everytime I connect my Amiga 1438S monitor, I Always get the same Guru error and my whoe Amiga crashes.
I use CPU cards 3630 and 3640 with 060 adapter. I also tried using Kickstart 3.1 and a patched version of Kickstart 3.9.
