Image rejected for technical reasons

Be sure, if this is a render, that the description says so. Adobe's customers become irate if they believe (from the small picture) that something is a photo, then they find out from the purchase that it's a render. 

I like the concept.  It's a shame it's too dark.

A Level Adjustment in Photoshop would brighten it.   See screenshot.

You have colour noise in the sand, and that's a standard defect:

Your 3d renders are vetted like photographs if they are photorealistic, so all defects that apply to photographs apply to your pictures.

This also applies to the histogram:

According to this, your picture is underexposed.