The executor relied on the advice of his accountant that the time period for both extending the time to file an estate tax return as well as the time to pay the tax was twelve months from the due date, disregarding the specific date on the extension form that the deadline for filing was six months. Generally, an executor who fails to file a timely estate tax return is subject to a late filing penalty unless it is shown that such failure is due to reasonable cause and not due to willful neglect. To establish reasonable cause a taxpayer must prove that he "exercised ordinary business care and prudence and was nevertheless unable to file the return within the prescribed time." The executor in this case argued that, by relying on his expert accountant's advice about the effect of the extension on the deadline for filing the return, he had exercised ordinary business care and prudence. The 9th Circuit Court of Appeals held that such reliance was misplaced and was not sufficient "reasonable cause" necessary to abate the late-filing penalties because it was nonsubstantive advice (i.e., not advice about substantive tax law).