I just got a d7100, and was looking forward to trying out the in-camera multiple exposure feature. In the menu, it stays grey and says option not available in current settings. I've tried changing a few things, but haven't been able to fix it. I tried changing to single shot mode, aperture priority, changed from raw to jpeg, metering to auto...I forget what else. What am I doing wrong? I also see that HDR is also disabled, if that helps. Thanks!