Hi. I was googling around and didn't find a thing about this bug, but anyway...
When I'm downloading any file from uloz.to on Linux I always got "java.lang.StackOverflowError". An error message will pop out with request to restart FRD but downloading will continue just fine.. I think you missing "catch(Exception e)" somewhere in your code..
Attached file was created as follow $ java -jar frd.jar --debug 2> frd.log

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define true false; //happy debugging

This is a known OpenJDK 6 bug. Please update to OpenJDK 7 (or Oracle JRE).