Sorry, my misunderstanding... I suspect you might be hitting the issue described here: https://github.com/opendatakit/javarosa/issues/405. Which happened when you had a calculation as the input date to a date funtion (format-date(), decimal-date-time(), ...), the javaRosa parser threw a bogus error.
What tool are you using to convert your form to XML? If using XLSForm Offline, have you tried disabling Validation?