Wrapped java.lang.IllegalArgumentException - BIRT

Hi,

I was trying to define a custom column in one of the Joint Data sets and I came across this error
Wrapped java.lang.IllegalArgumentException

The code I'm using is ,

var dt = new Date(row);
var day = dt.getDay();
if(day == 0){
var dt1 = new Date(dt.setDate(dt.getDate()));
} else if(day == 1){
var dt1 = new Date(dt.setDate(dt.getDate()-1));
} else if(day == 2){
var dt1 = new Date(dt.setDate(dt.getDate()-2));
} else if(day == 3){
var dt1 = new Date(dt.setDate(dt.getDate()-3));
} else if(day == 4){
var dt1 = new Date(dt.setDate(dt.getDate()-4));
} else if(day == 5){
var dt1 = new Date(dt.setDate(dt.getDate()-5));
} else if(day == 6){
var dt1 = new Date(dt.setDate(dt.getDate()-6));
}
(dt1.getMonth()+1)+"/"+dt1.getDate()+"/"+dt1.getFullYear();

Any help is appreciated

Thanks,
Bharath