That phrase gave me pause, too. Did you replace your optical cable with another optical cable, which then worked. Or do you mean you went back to the original optical cable after using the analog cable?
Regardless, I think it might be possible that the optical cable is damaged. I've not ever heard of an optical cable being intermittent, but I suppose it might be possible. Optical cables are made of glass fiber, and are much more easily damaged than a wire cable.
Or it may just have not been plugged in well on one end.