Well, the captions for all checkboxes except this one are numbers (codes) while this one is letters. However, since numbers are not valid for use as a name, the number is prefixed by the letter "a" for the object name and field name. For example, if the caption is "810", the object name and field name (and untimately the controlsource) for this checkbox would be "a810". For the errant checkbox, its caption, object name and field name are all "RNC".