DateTimeFormat.parseStrict()
expects a String and
addContDateCreateDateBox.getValue().toString()
returns 'Fri Aug 02 00:00:00 EEST 2013' which is not parseable according to the format you specified ("dd.MM.yyyy") in
private DateTimeFormat ft_big = DateTimeFormat.getFormat("dd.MM.yyyy");
Instead use
ft_big.format(addContDateCreateDateBox.getValue());
to format the date returned by
addContDateCreateDateBox.getValue()
After the date is properly formatted you can use the parseStrict() method to enforce the format is respected.