Nikon D90 Err message?

I was doing a Santa photo shoot yesterday for a local store with my D90. I knew that I was going to be going through batteries during the shoot so I used my vertical grip for the extra battery power. I was also using a 16Gb sd card in the camera. At one point the battery indicator started flashing on the top lcd panel on the camera. So I switched batteries and was ready to go again. As soon as I closed the battery cover on the grip and turned the camera back on, the top lcd panel started flashing "Err". I tried turning off the camera and waiting a few seconds before turning it back on, I tried removing the lens and putting it back on the camera as well. Still that Err message was there and the camera wouldn't function. I had changed nothing but the batteries and this caused the Err message to pop up. So I decided to switch memory cards and suddenly the Err message disappeared and the camera was ready to go again. So I figured that the memory card was full and that was what had caused the Err message to appear. However when I returned home and checked the 16Gb memory card I noticed that there was only 45Mb used. Any idea what might have caused the Err message?

Which lens are you using? If it is an older lens check the aperture ring. If the ring is set to anything other than closed all the way down, then it will not function properly and will show an Err message on the D90. Make sure it is set to the orange aperture value and use the locking switch to hold it in place.

I would also agree the lens was likely the problem. However if you are using a off brand SD card you can encounter wright problems. You can get off-brand batteries that will not work properly, cause heat and cause the camera to want to cool down. If you use live view for a prolong time it will cause a heat problem and cause the camera to error.

If you could provide info like:
Lens used:
SD card used:
Battery(s) used:
Settings the camera was set at (A, M, S, P, auto):
On camera flash or wireless type:
Was Live view used:
Did you use a shutter release

"Err" usually appears if the camera has experienced a mechanical error, is usually caused by a low battery, and is usually resolved by *pressing the shutter release button*.It will go through the shot cycle without recording the image. If operation isn't restored, then you should take the camera in for repair.