QNX4 + SBS V5C + VME

I am using QNX4 on a single board computer = SBS V5C. This board has a
built-in VME interface and SBS supplies a QNX4 style VME device manager
and API.

Anybody got any ideas how why I might be able to access some VME boards
without error while other boards seem to fail? I know the “failing”
board is being addressed correctly and that it works in a different
environment (VMS + DEC Alpha + Bit3 PCI-VME bridge). I’m looking for
some trick or gotcha.

Thanks.