The accesory that is configured in MAX (and that I'm using) is the SCB-68.
I opened the 6533 text pannel in MAX and read/wrote to/from the digital lines without errors. Mind you, this only tests ports 0, 1, 2, 3 but port 4 cannot be tested.
I used the "Write to 1 Dig Port (653x)" VI to test the same thing. I was able to write all ports (including port 4 by wiring a "4" to the Port Config VI) without errors.
I've narrowed down my problem to one particular VI. (see attached file). If I run it with the "Highlight Execution" (lightbulb) on, it runs without a problem. When "Highlight Execution" is off, I get the -10440 error!?!?!