Preloader

Why does the following work:

bytesTotal = _level5.getBytesTotal();
bytesLoaded = _level5.getBytesLoaded();

and the following does not:

bytesTotal = eval("_level"+_root.levelNum).getBytesTotal();
bytesLoaded = eval("_level"+_root.levelNum).getBytesLoaded();

whereby _level5 is created using variables

Any ideas???
Any help will be much appreciated !!
Thanks
John