I had the same experience you did and checked the roots and they were fine. Shortly after that, I read in a book that it is not uncommon in this genus for a mature plant to send up their first spike and not be able to sustain it. So once the buds start to open it totally saps the strength of the plant and the bulb shrivels. It was exactly what happened to me.
Most of the advice I received was to cut the spike off and hope to rejuvenate the plant. But that was too heartbreaking....hope yours turned out better.