‘(a) an insufficiency of funds is not a reasonable excuse, unless attributable to events outside P’s control, (b) where P relies on any other person to do anything, that is not a reasonable excuse unless P took reasonable care to avoid the failure, and (c) where P had a reasonable excuse for the failure but the excuse has ceased, P is to be treated as having continued to have the excuse if the failure is remedied without unreasonable delay after the excuse ceased.’