At this point, I'm not sure what you mean. first you say that the NI controller and MAX 'works good', then you say an Agilent controller works good, and then you say the NI controller doesn't work. How can the NI controller both work and not work?
Unless you have the NI-GPIB driver loaded, you will not be able to use the low level GPIB functions. These are what MAX uses to detect an instrument. You may be able to use VISA but I don't understand why you would want to have any Agilent driver software installed if you are planning to use an NI controller. I think you are having a conflict between the two that will probably go away if you clean everything up (uninstall both NI and Agilent drivers) and then just install the NI drivers.
