problems applying dissolve transitions 10.3.4

I`m trying to drag a dissolve transition between these two clips, its working on all the other photos, but not between these two. I keep getting the pop up warning, however when I click apply to go ahead nothing happens, the transition is not applied. all my photos are sometimes different aspect ratio but thats not stopping the other transitions.

I did use D to overwrite a previous photo with the new photo

I can actually see a few frames of something between those clips. Zoom in on that edit point more, you'll find your issue.

ah great thankyou, yes I fixed it now. cheers.