Rule 25(19) of the Family Law Rules gives courts jurisdiction to change 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, if an affected party was not present when the order was made because the notice was inadequate or the party was unable, for a reason satisfactory to the court, to be present.
This section, however, does not correct errors in law or mistakes in law as such errors fall within the jurisdiction of the court of appeal.
http://www.canlii.org/en/on/laws/regu/o-reg-114-99/latest/o-reg-114-99.html