Eucharist
A prime example of valid but illicit celebration of a sacrament would be the use of leavened wheaten bread for the Eucharist in the Latin Rite, or leavened wheaten bread in certain Eastern Catholic Churches. If, on the other hand, rice or rye flour are used instead of wheat, or if butter, honey, or eggs are added, particularly in large quantities, the Mass would be invalid and transubstantiation would not occur.
A priest who has been laicized or suspended or excommunicated is not to say Mass, but their Masses are still considered valid.
Read more about this topic: Valid But Illicit