Copying the TandemVids directory is not the correct way to reinstall TandemVids.
I would recommend uninstalling TandemVids using Add/Remove Programs. Ensure the "C:\Program Files\Swoopware\TandemVids" folder has been completely removed and then installing it again. There are no settings stored in the installation folder. If any files have newer dates due to the copying, the installer won't replace them, which could cause mismatched versions of the YouTube api files.
Windows 7 has reached end of life and will no longer be supported.
This forum post has the procedure for moving TandemVids to a new computer.
I can't shed any light on the 401 error but
this forum post may help.
I am aware of the quota exceeded issue. Google have transferred most of the TandemVids quota to the new RunRunVids application, which will be released shortly. The quota battle is the reason for the delayed release of RunRunVids. If you are seeing quota exceeded, so is everyone else currently using TandemVids to upload to YouTube. The only option is to wait and try again later. The quota is reset every 24 hours and is usually enough to handle the TandemVids traffic. As more people switch to RunRunVids, the TandemVids traffic will be reduced.
Mick