Hello, Were there any final thoughts or resolution on this elderly thread, as a newcomer to the site I have just found it?
I often get this message but I have had it with Vista/7 32 bit and 64 bit. Also happens with D200 & 700 and so I do not think it camera or OS specific. I have done as (I think it was) the very nice Jason Odell suggested somewhere (sorry cant remember where) and 'cleared the cache folder' to no avail. It is not in my case specific to file ext either have tried with JPG/NEF/TIF
In my case the problem usually goes away if I cancel NX2 for some minutes then try again.
Hard to trace because it will eventually work OK even with the same image that originally failed to save.
I have read on the web the other people actually lose their NEF ie it is deleted but I have not had that problem.