It is generally an emergency condition. Various factors can cause egg binding, and the condition should really be a sign of other disease rather than a disease in and of itself. Oviduct infections - This is really self explanatory. Infections of the oviduct are common. Infections result in scarring to the oviduct, resulting in egg binding.
Infections can also result in delayed or rapid passage of the egg through the oviduct.
A pus-filled oviduct can also result. This is also called a pyometron. Other disease - Any other disease state that results in weakness, especially at a time of excessive demand, must be considered. This can be any chronic disease you can think of, and these must be ruled out in any examination. I would look at providing a balanced diet in the form of pellets or crumbles.