http://jdownloader.org/feed.php?mode=list&type=rss2&linkto=page&ns=news:blog
The new AVG Version has a feature called “linkscanner” that causes downloaderrors. JD reports CRC-errors or the extraction fails.
Downgrade to AVG 8.5 or disable the Linkscanner
Thx to fprietog for reporting the bug an providing this solution