Texture is not readable
When you try to share texture, you get error like:
I/Unity ( 2816): UnityException: Texture 'shareDefaultTexture' is not readable, the texture memory can not be accessed from scripts. You can make the texturereadable in the Texture Import Settings.
It means that texture is locked and Unity cannot read pixcels from texture, you should mark texture as readable in the texture import settings.
Open Unity Inspector Tab and select the texture.
Switch Texture Type to Andvanced and enable Read/Write Enabled checkbox.