If it's a .capx, try unzipping it to a separate folder and look in the Textures folder for the missing texture referred to. You can add any texture with the same name, and it will then be able to be opened, provided there isn't any other problems.
If there are numerous errors, or the textures and other folders are missing entirely, then you will have to fall back to an autosave or backup.
This also assumes you have setup the autosave and backup options. If not, then that's a very painful lesson, unfortunately.