Rule 25(19) of the Family Law Rules provides that a motion may be brought to change a court order which:
(a) was obtained by fraud;
(b) contains a mistake;
(c) needs to be changed to deal with a matter that was before the court but that it did not decide;
(d) was made without notice; or
(e) was made with notice but the notice was inadequate or the party was unable to be present
http://www.canlii.org/en/on/laws/regu/o-reg-114-99/latest/o-reg-114-99.html#sec15subsec14_smooth