Pay attention and you’ll frequently see and hear people use “reoccur” and “reoccurrence” to describe something that has happened before. Logically, they are correct: an act has occurred and then has happened again, so you would think it had re[again]occurred. But, in fact, the grammatically correct forms are “recur” and “recurrence.”
If you are guilty of this offense, please avoid engaging in further recurrences. Your readers and listeners will thank you.
WordThoughts 