Alright, I asked this on StackOverflow (here) and they suggested trying ServerFault to get help on permissions.

So here's the deal. We designed a custom PCI card and wrote the driver for it. It's been working for years without problems but now we encountered one particular installation were it doesn't work. The problem is that we cannot connect to the PCI to begin communication with it.

We tried replacing the card and had the same problem. We had the motherboard replaced thinking the PCI slots were bad. That didn't help either. We tried the cards in a different computer and they all worked. So it seemed to be something specific to the computer.

The Windows Device Manager indicates the device is working properly and seems to have all the correct driver info.

We now have this troublesome computer back at the office for testing. With the help of some extra debug info in the driver we determined that we cannot connect because access is denied. Sounds like a permissions issue to me.

I should note that we are logged into the system as a local administrator.

So what configuration option in Windows can prevent access to a device?