There can be multiple causes for this. First, make sure you are using the latest version of YTD by opening the program and going to "Help" > "Check for updates".
If you receive a "Pause, waiting for internet connection" or "Failed 6" error please perform the following actions: Regardless of your default web browser, reset your Internet Explorer settings by going to "Tools" (Alt + X keyboard shortcut) > "Internet Options" > "Advanced" tab. Select "Reset", making sure to choose the "Delete personal setting" check box.
YTD's connection can be blocked by your antivirus or firewall. Make sure to add YTD to your firewall's list of allowed programs. If the issue persists, try switching your Antivirus and/or Firewall off and try using YTD again.
As a final solution you can uninstall YTD. Run a registry cleaner program and reinstall YTD.