I don't have much personal experience, but I have run into this one already. On my first orchid even.
Stupid root rot. I thought they were dropping because I transported the plant in the cold and my beloved husband forgot to cover them before taking them to the car. After the buds all started dropping (2 weeks after I bought it) I popped it out of the pot and found a war zone.
Just to be safe, check your roots, if they look good and your culture is all as it should be go with the cold or just not ready theory.