First verify the version of Quik Invoice for Windows (6.2B or 6.5A). Next check the format the date field in the specification. Lastly, check the regional settings in Windows for dates.

Please make sure that the Windows settings has a 4 digit year; this is especially important if you are running older versions of QIWin 6.2B. You probably also want the date field in the spec to be a 4-digit year format as well.