Usually, there are two likely causes for issues like this.
1. The usbtmc driver is claiming the device. To diagnose it, see if you can do "rmmod usbtmc" as root and run the utility. If the device then shows up, the usbtmc module was claiming it. If you unplug the replug the device again, the usbtmc module will claim it again, so if you want to use NI-VISA to control this device, the solution suggested above to blacklist the usbtmc module might work for you.
2. The device is only accessible to root. To diagnose this problem, see if your device shows up when running the utility as root. This would mean that the udev rules that are installed by NI-VISA installer for the usbtmc device is not working. If you can see the device as root, then you can run the "/usr/local/vxipnp/linux/NIvisa/USB/AddUsbRawPermissions.sh" script. First use lsusb to get the vendor and product IDs of the device and then run the script and provide it the IDs in the format shown by the instructions. After doing this, if you unplug and replug the device, it should be visible as non-root.
Please note that you might have to do both of the above (rmmod usbtmc and run the utility as root) if both of these issues are affecting your device. Let me know if neither of these suggestions work and I will look into it further.
EDIT: corrected the path to the script.
