Parse Exception : java.text.ParseException: Unparseable date

I have inherited a UDF in some mapping that on the whole, works okay...

but it throws an error after mapping a few dates:

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-18T00:00:00.000Z"

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-23T23:59:00.000Z"

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-18T00:00:00.000Z"

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-23T23:59:00.000Z"

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-18T00:00:00.000Z"

Parse Exception : java.text.ParseException: Unparseable date: "2010-03-23T23:59:00.000Z"

the first few map okay... then i get the exception.

the UDF is as follows:

public String convertDateTimeToUTC(String strDate, Container container) throws StreamTransformationException{
AbstractTrace trace = container.getTrace();
Date date=null;
SimpleDateFormat sdfSource = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
try{ 
String dt = strDate; 
date = sdfSource.parse(dt);
trace.addInfo("Local Date:"+date);
SimpleDateFormat sdfDestination = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
strDate = sdfDestination.format(date);
}
catch(ParseException pe){ 
trace.addInfo("Parse Exception : " + pe);
}
return strDate;

can anyone see why this fails after successfully mapping a few fields???