Sprite Editor Problems

I've noticed that the sprite editor no longer works for me; I have a PNG with the import settings of type Sprite, filter mode Point, mode Multiple and format Compressed, but when I open the sprite editor I don't see any of the content of the PNG, and slicing won't work. I noticed that if I open up older textures in the sprite editor that worked previously they will now have the same problem, in that the sprites don't show in the sprite editor at all.

When I try to reimport the PNG, I get a number of "FAILED(hr)" errors in my console output.

In addition, when I try to set a TextMesh's font to a bitmap font that I've imported, selecting the TextMesh's GameObject will no longer update the inspector window with its info, so I effectively can't edit that TextMesh. The font in question is a freeware font I'm using for testing that can be found at http://www.dafont.com/04b-30.font?back=bitmap.

Any help would be greatly appreciated.