This sounds very much like a Jdownloader bug. I have experienced the problem with different hosts. The error just suddenly appears after downloading at least 80% of the file.

Given that this is not a permissions or space issue, I would guess the error message is misleading to the actual problem.

It seems that this thread is pretty old, so the problem has been around for some time. I am running on a MAC , ML. Other folk are experiencing this on Windows.

Is there a way to turn on some extra debug info - I dont' see the errors reflected in the error_log