http://www.youtube.com/watch?v=pfhjJ00IuW4

Make sure you are using the latest 4.1.2 version of the application.
If you have an antivirus program of a firewall, please try to disable them and after that paste link to a video in 4K Video Downloader.


If this fixes your issue, please add our application into the whitelist of your antivirus\firewall in order to stay safe while browsing the net and also download without interruptions.
If it doesn't help, try changing directory folder in Smart Mode settings, then try to download something (both with Smart Mode turned on and off).

If none of the above works, reinstall the application.
Delete 4K Video Downloader and all associated data from your computer.


Please make sure you have deleted all the data associated with the application from your computer before installing a 'new' version.
If your computer operates on Windows, don’t forget to delete information also from Windows Registry (menu > search 'regedit) > run command > find 4K Video Downloader folder and delete it).


If you are on Mac, do the following:
Go to Finder, press Alt (Option), then proceed to the menu Go > Library. Find the folder Preferences and delete the file com.4kdownload.4K Video Downloader.plist


Then reinstall the application and launch it, see if the error repeats.