When the pump runs until the ABS light comes on, it means there is no pressure being held in the system. After pumping for about 2 minutes, it will give up and stop, tripping the ABS light.
Possibly the unit had enough pressure even though the reservoir was empty. If you had activated your ABS, this problem would have manifested itself.
Bottom line: You have a sticking internal ABS solenoid that won't unstick. It's mainly caused by age and non-use of the ABS system.
There are only 2 soultions.
Go out to a safe location and continuously lock up your brakes activating the ABS as much as possible--at least 20-30 minutes of locking the wheels up. This should free the solenoid at least for the day.
If the problem persists after a few lock-up sessions, you need a new ABS unit, my friend. :frown:
New is about $1,800, 
so you want to find a used one if possible. You should be able to find one in good shape for $300-500.
If you want to read more, here:
http://www.nsxprime.com/forums/showthread.php?t=46983&highlight=abs+pressure
Here's an ABS unit for sale but condition/age unknown. Super cheap, though:
http://www.nsxprime.com/forums/showthread.php?t=58876&highlight=abs
