lol i had the same problem. once it downloaded the update and then restarts hit cancel,then you should see two update things already in ur downloader.select thos and download. or just delete the two files you have there. restart and see wot happens,it might try and do the same thing again.but just hit cancel and delete the two files in the downloader.try and download something and see if it works.
make sure you sign in ur premium account first lol.
you could also use speed downloader.thats wot i been using instead of jdownloader. the last update of jdownloader wasnt working for me.but was on parallels on xp? go figure lol