Having trouble with dragging sprites into the tile palette

Hi there,

I’ve been trying to drag sprites into the tile palette manager, but for some reason it just won’t let me. I tried doing it earlier and it worked, but now it’s throwing a pretty generic error message. I upgraded to the latest version of Unity and it got rid of the error message, but it’s still not letting me drag the sprites into the manager. Any thoughts on how to fix this?

Here’s a video to help show what exactly is going on:

I had this problem because the png file I was using for my sprite was smaller than 256x256.
I’m still looking for documentation that explains why this is but I wanted to mention it for anyone else with this problem.