Yes. You must be staying in a Disney resort, you must have a multi-day ticket (Ultimate Park Hopper, Seasonal Pass, Annual Pass, Park Hopper, etc), and you must have used your pass on the day of the E-Night in order to gain entry.
I believe it is so that you aren't getting into the park for just $12... I know it sounds crazy, but that is their way of controlling how many people "can" go during that time frame. I also want to say that (I think) they always had that as a stipulation for the E-nights...