This problem seems to have started several months ago. Sometimes I could download, sometimes not. Previously I have downloaded hundreds of movies with no problem.
One popup now states "Credentials Required". Although I am logged into vk.com as a user, the credentials page displays my username and password, but still will not save the file. I have tried Auto and manual modes and both monitors. Any suggestions. For what it is worth, here is a sample file that will not download. Not sure if you need to be a vk.com registered user.
https://vk.com/video-98421875_456240529