Thumbnail screenshot issues

I used to be able to delete my screenshot thumbnails and move them to trash. I can no longer do that. When I try and delete or move to trash a thumbnail screenshot I now get the message, "The operation can’t be completed because you don’t have permission to access some of the items." What is this all about? But, how do I delete or move a screenshot thumbnail to trash now? I see the screenshot is now "locked". Don't know how or when this happened? Maybe something I did and didn't realize what I had done? I also see "finder" has some play in this issue because I also can't delete the screenshot when I go to the finder app where I can see the same screenshot thumbnail. Can someone please help. Sort of weird situation I didn't have before when I could delete my screenshots thumbnails I had on the right side of my monitor.