Unreadable texture
Message
Unreadable texture.
Explanation
Sometimes some of the assets (textures included) get damaged for various reasons: artist errors, broken merges, file system or software failures. Whenever the Playable Plugin attempts to export a texture and is unable to get its pixel data.
Can it be simply "Read/Write" disabled?
Not really. Playable Plugin is using multiple techniques to gather texture data, starting by making a copy of the underlying texture source file in case it is PNG, up to utilizing Unity's Graphics API to copy pixel data to work around compressed formats. Thus, if Playable Plugin fails to extract pixel data from a texture, it is most likely damaged in one way or another.
Not really. Playable Plugin is using multiple techniques to gather texture data, starting by making a copy of the underlying texture source file in case it is PNG, up to utilizing Unity's Graphics API to copy pixel data to work around compressed formats. Thus, if Playable Plugin fails to extract pixel data from a texture, it is most likely damaged in one way or another.
Steps to fix
Fix the underlying asset.