The attached patch seems to get things working again for machines that believe they can do environmental event machine check handling but really can't. The checks will only be enabled for systems with OVMS 7.2 and later (determined at compile time) and where bit 5 of CRD_CONTROL is set (determined at run time [thanks again, Carl]). Since I don't have access to any machines that *can* perform these checks, testing is left as an exercise for the hardware-endowed.
vms-system.patch