Isn't 64 kind of low for an ale? The lower the temp the longer the fermentation...
EDIT: I just found this:
The Nottingham strain was selected for its highly flocculent (precipitating) and relatively full attenuation (transforming sugar into alcohol) properties. It produces low concentrations of fruity and estery aromas and has been described as neutral for an ale yeast, allowing the full natural flavor of malt to develop. Good tolerance to low fermentation temperatures, 14°C (57°F), allow this strain to brew lager-style beer. Recommended 14° to 21°C (57° to 70°F) fermentation temperature range.
So, I guess you are in the zone...