@shoval23089
Can't you move the photo in build mode?
My guess is that that one photo has become detached from the sim or household that took it. Probably because the sim who took it has either died or moved or the photo has lost it's connection to the household somehow. And only a household member can copy the photos too, so you don't get the option for other sims.
I've run into this. I built a museum lot to house a lot of my sim portraits. Then I sent a sim from each household there to place their portrait photos. What I found was that only the household that took the photos and placed it in the museum could move them later on. Sims from other households could not grab or move them but they could move theirs. But I was able to rearrange them in build mode.
Hope this helps.