It looks like the firmware has already loaded successfully by running fxload twice.
You would not see "SerialNumber: MY56153375" if the second fxload was not successful. Also, idProduct=0518 changes to idProduct=0718 after the second fxload. All three LEDs would normally be lit at this point, which is what you're seeing.
In this state, it's time for "gpib_config --minor 0" (NOT fxload). After that, only the green READY LED should be lit and the adapter is ready.
I tried running fxload three times like you seem to be doing, and I get the same single FAIL LED, and the same "device descriptor" errors.
You shouldn't need to manually run fxload anyway. Your hotplug script, /etc/hotplug/usb/agilent_82357a, should be doing everything for you, including the gpib_config.