The "security token" message leads me to think that an HTTPS: or SSL: connection was attempted, and one end (either yours or the forum's) doesn't satisfy the requirements of the other.... it could be an expired (and not updated) security certificate, a no-longer-accepted hashing method or similar beastie.
I must admit, i can't recall ever seeing an attached video in a posting... have you succeeded in uploading one in the past?
As far as i can tell, CJPJ's problem was that he couldn't even upload the file to the forum.
The error message complains of a token problem.
(which i'll take to mean that it was happy with the file type)