I just don't see what is wrong with this image. It is a pano, so it is a large file.
My only critique would be that there might be a distracting lens flare in the top left corner (I don't mean the rays from the sun-which is lovely).
What was the rejection reason - exposure?? I think the bottom of the picture is a bit too dark. Try lightening it up a bit. You don't really want solid blacks in your pic. And yes, maybe the lens flare as well- clone that out if you can.
Might be really the details in the trees (underexposure). Seems like the details are lost. Too much and flat black, if you
understand what I mean.
Thanks - good suggestions. I will make changes and resubmit.
It is possible that there is too much noise or too busy. They will also reject images that have been processed too much as well. It is a beautiful panorama, also not something they may be looking for.