At once nostalgic and satirical, Late Nite Catechism walks a fine line between the saccharine, soporific Nunsense and Christopher Durang's bitter Sister Mary Ignatius Explains It All for You. At least Vicki Quade and Maripat Donovan's mildly barbed look at Catholic education appeals both to lapsed and practicing Catholics. Which is why, I suppose, this affectionate, witty play is still running after all these years. And because it's essentially a one-woman show, it depends entirely on its lead actress for warmth and comic range, for embodying all our ambivalent attitudes toward the foibles and follies of the American Catholic Church. She must also be someone with the patience to teach the audience about Catholicism, which is very important when it comes to clueless people like me who always confuse the Immaculate Conception with the Virgin Birth. Patti Hannon didn't originate the role--Donovan did--but as the sister at the center of the play she definitely has the maternal/teacherly edge that will win both our affection and respect. Ivanhoe Theater, 750 W. Wellington, 975-7171. Open run: Fridays-Saturdays, 7:30 PM; Sundays, 2:30 PM. $15-$18.