you have now experienced a hypertonic situation in your back. ie you have too much tone in your back, it is tight!
you did what many on here said to do...strengthen your lower back with good mornings, deadlifts, etc but neglected to stretch it...so, now it is in a chronically tightened state. when you crunch up...it stretches it. i would venture to say that when you do reverse crunches it hurts or feels like its pulling.
now you have taken 2 steps forward, now time for 1 step back. you have to stretch your lower back extensively.
there should be no reason why you should fear doing crunches if you take the necessary steps to fix what you have created by misinformation. this board is notorious for one sided pieces of advice. this is a prime example.
stretch stretch stretch. before and after your workouts now. it will go away rather quickly but you have to put the time in or you will just make matters worse and end up pulling something by trying to work through and do abs. not saying dont do abs but keep the motions as far from fast and ballistic as possible for now until you get some flexibility back.
peace.