I've already been accepted to submit film on deviantART and still can't submit film files, can you tell me why?

You have to activate your film privileges by clicking the link in the note that was sent to you in your message center that lets us know that you received all of the information regarding your new film privileged account. If you didn't activate your privileges and no longer have the note, please contact the help desk so that your invitation can be reissued.