Using a File Property "modified.getTime()"

Wrote this script

///////////////////////////////////////////////////////////////

var f = File('D:/Proba/Dest.psd');
IniData = f.modified.getTime();
do {
var CarData = f.modified.getTime();
//~ $.writeln(CarData);
} while (CarData - IniData == 0)
$.writeln("file was Changed");

//////////////////////////////////////////////////////////

want to execute it AE

Pay attention to the commented out line

     //~ $.writeln(CarData);

If you remove the comment from this line, the script works fine.

If you execute the script with a comment on this line, then after saving the changes to Dest.psd , an error occurs. How to explain such behavior of a script???