Sorry for these issues. I'll need a bit more information to reproduce these errors.
1. Video - are you uploading video file or linking to some site (like youtube)?
2. Do you receive 406 error when clicking 'quote' or when submitting reply?
Hello and welcome to Science Forums / Hypography! This is usually caused by malware software installed on your computer. If you're on windows you can try scanning your PC with microsoft's free tool : https://www.microsoft.com/security/scanner/en-us/default.aspx