@pocs,
Please make sure you have the latest version of the download manager as our site is constantly being updated. Your download manager will have to be updated as well.
If you are certain you have the latest version, you must now contact the support team for that specific download manager. Notify them of the problem and they will resolve the issue (usually within a timely manner) and in the mean time you can download directly from the website.
For issues related to Internet Downloader Manager (IDM), please refer to their help guide:
http://www.internetdownloadmanager.com/support
For issues related to JDownloader, please refer to their support:
http://jdownloader.org/