Where is my render?

G'day All,

I added a new render to my gallery yesterday, The Well 02 (My original is called The Well 03). It uploaded as per usual but then the thumbnail was replaced with little symbol.
I tried deleting that render & uploading it again today but the same thing happened.
The content is similar to other pics that I have uploaded & fits within the guidelines for the site.
The only thing I can think of that might cause this is the file size.
I've attached the file here.
Any ideas?
Cheers