I have also been having this problem with the access lamp flashing on and off. After reading this and other posts re third part battery grips, I took off my Pixel grip and los and behold, the lamp no longer flashes. Rather than risk draining the battery (as some people have reported), I've bitten the bullet and ordered a Nikon MB-12 grip. Heigh-ho, the Pixel grip works fine, but if it's going to drain the battery that rather negates half the point of having a battery grip in the first place...
D800, D700, D300
It ain't so much the things we don't know that get us in trouble. It's the things we know that just ain't so.
Why is this thus? What is the reason of this thusness?