What fonts does ToDo X require?
Although you can change them in the Preferences, the usual fonts are Lucida Grande Regular (for display) and Helvetica Regular/Bold/Oblique (for printing). Some special characters used by ToDo X, such as circled numbers and checkmarks, aren’t present in those fonts and will be obtained via font substitution. They’ll typically be drawn from Zapf Dingbats or AppleGothic Regular. If you think you might have a font problem, check the font sample here.