Shared a folder link with 4 vid clips in with a few friends, have used Dropbox for years, no issues until now, and banned?
If its your first ban it will automatically clear within 24 hours or so. However, each one does take longer.
Dropbox limits users bandwidth on links to 20/gb a day across every link for free users, so, if you used over that (maybe the 4 watched more than once etc.) that will result in a ban.
What exactly is the error?