[amibroker] How to relate a date to barindex

[tipequity]

I am trying to find the date for 252 bar ago. I have written the 
following code. However, it does not work! any suggestion is much 
appreciated. TIA

SetBarsRequired(10000);
BarIndx = BarIndex();
aYearAgo = BarIndx - 252;

AYearAgoDate = LastValue(ValueWhen ( BarIndx <= aYearAgo ,DateTime()));
_TRACE("AYearAgoDate: " + NumToStr( AYearAgoDate));

Title =
"BarIndex: " + BarIndx 
+ " \n" + "aYearAgoBar: " + aYearAgo 
+ " \n" + "A Year Ago Date: " + WriteVal( AYearAgoDate , formatDateTime)
+ " \n" + Interval(2) + " - " + Date() ;