When the Ant task doesn't find the specified icon, the error message reads "Icon doesn't exist".
It would be very helpful if the error message included the absolute path of where the icon has been expected to be.
the issue was copied to http://code.google.com/p/jliftoff/issues/list
fixed. Will be available in jLiftOff 3.0.3 http://code.google.com/p/jliftoff/issues/detail?id=44#c1