Using non activated free version of 4K Video Downloader. I think it is version 4.9.

Using desktop PC with Windows 10 64 bit.
Usually use Chrome browser.

Had been downloading a lot of YouTube content, with no problems. Nothing changed, but suddenly I began getting error messages.

These all happened on YouTube.

"Can't parse this link. Please send it to our support and we'll check it"

"Error"

"Error. Unknown site"

"This site is unsupported"

After these errors happened, I was able to easily download from Vimeo, so this is some kind of YouTube issue.

Things I have tried without any success:

1. Run 4k as Administrator.

2. Uninstall and reinstall 4K

3. Run in Smart Mode. Run without Smart Mode.

4. Changed destination file of downloads.

5. turned off Firewall and other antivirus.

6. Rebooted computer.

7. Used Jailbreak VPN to connect.

8. Tried downloading with FireFox instead.

Nothing works. Nothing.

I am not logged in as a YouTube account, just public browsing.

I can't post comments on Youtube any more, or create playlists, I was banned, but can still watch. But that wasn't stopping me from downloading until about an hour ago.

Advice says to "check privacy settings" but that is meaningless to me, I don't know what it is or how to do it.

Also the Proxy suggestion allows you to LOOK at the page of Youtube, but video WILL NOT PLAY when using the proxy, so that's useless.

What I can't understand is how the hell YouTube recognizes me even when I'm accessing via a VPN?

I should also mention that something strange happend with 4k.
It WAS downloading all in MP FOUR format, which was a pain.

I don't know what I did or changed.
But suddenly the windows that showed choices for video definition didn't pop up any more, and everything was just automatically downloading as an MP3, I didn't have to keep hitting the "Extract" button any more.

This was going on when I was heavily downloading with no trouble, and it is still true now.

As stated above VIMEO downloads flawlessly with no errors. Other sites say "Unknown site".