1. Make sure the clipboard monitoring feature is activated. The clipboard monitoring icon is located on the menu bar. It is shaped like a clipboard with a check mark in the lower left corner. If the icon is not surrounded by a darkened square, the clipboard monitor is not active. Left-click the icon to activate it.
2. Update to the latest version of JDownloader. Left-click the globe shaped icon on the menu bar to check for any updates.
3. Uninstall and reinstall JDownloader.