I just upgraded to the 3.8 (built 1173) version and I'm still having problems downloading videos in an .flv version from YouTube (for example: https://www.youtube.com/watch?v=IaQd3wh9lDM). I see the message: Access denied. Invalid user name or password, even though there are no restrictions listed at the site.
Usually you cannot resume or restart downloads from random links generated by server-side. The links are valid only a short time - maybe 1 minute, maybe 1 hour. Sometimes they are valid only during a session opened in a browser so you can't even leave the download page.
Your question was answered more than once here. Just search and read more topics before asking, please.