Have you tried searching among your project if there is any where that is using/linked to "Sprite281"? CTRL-SHIFT-F and run a search for that name. Your output console will show where, if found, remove it. Because that message meant Sprite281 is linked to another instance (e.g. parent-child relation), etc.
If there isn't any, then maybe try create a new sprite, give it that exact name (same lettercase, etc.), then you delete it, see what message get shown if any. Lastly you could do a cache clean up (broom icon).