I also have a MaxDome and was initially plagued with dome errors. I ditched my USB-serial converters and instead install a PCI serial card. I have not had any problems with the dome since I did that.

The other thing to check is your shutter antenna. I initially just used a loop of wire like in the Max Dome documentation. That proved to not be reliable. I replaced the loop with two loops of wire each circling the entire dome. You can monitor for poor signal by looking at the lights in the shutter controller.

I debugged this all pre ACP so I know this was purely hardware.