When does a cause of action for solicitor's negligence accrue?

Lipson v. Cassels Brock & Blackwell LLP, 2013 ONCA 165 holds:

[73] In our respectful view, the motion judge's conclusion about Justice Le Dain's holding in Central Trust Co. v. Rafuse is incorrect. Justice Le Dain did not hold that "the limitation period for the claim of solicitor's negligence commenced running with the manifest challenge to the mortgage". Rather, he concluded that the earliest date on which the claim for solicitor's negligence could have commenced running was the date on which the validity of the mortgage (and therefore the validity of the solicitors' opinion) was challenged.

[74] Because the applicable limitation period for solicitor negligence was six years when Central Trust Co. v. Rafuse was decided, it was unnecessary that Justice Le Dain go further and determine the actual date on which the limitation period commenced – the action for solicitor negligence had been started well within six years after the earliest date on which Justice Le Dain found the cause of action was discoverable.

[75] In Kenderry – Esprit (Receiver of) v. Burgess, MacDonald, Martin and Younger(2001), 53 O.R. (3d) 208, at para. 19, Molloy J. recognized that Central Trust Co. v. Rafuse is not binding authority for the proposition that the limitation period in an action for solicitor negligence begins to run on the date of a manifest challenge to the solicitor's opinion.