Hi Tom,
Here is what I understand your issue to be:
When the USB hub is plugged into the USB port then the USB devices re-enumerate, sometimes changing the Dev# previously assigned to the devices. In your application you are using Dev1 specifically for tasks, Dev2 for other tasks, etc.
Does this happen every time? Does this happen if you plug the USB-6008 or USB-6501 in by itself?
What version of DAQmx do you have installed? The latest version is 8.6 and
can be found here. Are you using DAQmx or DAQmx Base? If this is a WinXP machine you should be using DAQmx not DAQmx Base.
You can
programatically determine the USB device serial numbers & Dev #, you would then use that information to setup your tasks correctly no matter what Dev# is assigned to the devices.
Here's how you might do that:

Here's a screenshot of the front panel:

Please do post back with DAQmx version, if it occurs with just a single device, any more relevant information you might think of. Updating to the latest version of DAQmx is always a great idea.
Have a great evening,
MatthewW
Applications Engineer
National Instruments
Message Edited by Matthew W on
11-04-2007 07:38 PM