Dragons will not be eligible for disenchantment if either of the two conditions apply:
1- You do not have 6 or more dragons. Players cannot disenchant a number of dragons that would drop the total of their remaining dragons to less than 5.
2- The dragon you want to disenchant was one you used as a parent to breed an egg – and that egg has not yet hatched. Whether that egg is currently incubating with a timer or just sitting in your nest waiting for its turn to hatch, neither of its parents can be disenchanted until it hatches and the new dragonling is born.
Why can’t the parents be disenchanted? 
We’re not entirely sure.
Dragons are, by nature, very mysterious creatures. We think that maybe they are busy guarding the egg? Sitting on it to keep it warm? Maybe not the ice dragons… In any case, once baby dragon meets parent dragon, we know the parent dragon is ready to move on! (and be disenchanted)
