Cymbidium flower buds blasting ... why?

[Tropic]

My Cymbidium plants are growing strong and healthy and all were producing flower spikes. As soon as the spikes were about five inches long, with some flower buds developing, the buds changed to a yellow color and blasted. Eventually the flower spikes all went yellow and ceased to grow. They all became black and I therefore removed the now dead material. I am wondering why this should happen and what can be done to have some flowering success.