fixed, try now.
This issue has been addressed and fixed, you will need to wait for updates to come out for 0.9.581 (stable) / old NIGHTLY. These older versions update process is controlled manually. We try to update every 0-14 days (but some times longer).
or
use JDownloader 2 (this version has instant plugin update system), and wait no more!
JDownloader 2 install instructions and download link
http://board.jdownloader.org/showthread.php?t=37365