Maximum Windows 7 RAM with VDGA PCI passthrough?

Hi, when I try to assign a VM a PCI passthrough GRID card and power it on, it fails if I have more than 32GB of RAM assigned to the VM. The error message is:

An error was received from the ESX host while powering on VM V470.

Failed to register the device pciPassthru0 for 7:0.0 due to unavailable hardware or software support

If I decrease the RAM to 32GB, it powers on fine.

Is this related to the pciHole.start setting? Per the documentation, I have it set to 2048, but do I need to change that for VM's with more than 32GB of RAM?

Thanks.