Mother of god, how do I stop this? I've been trying to post on a website which shall rename nameless in my own interest, and I keep getting this fucking error. Here's how it goes:

>Go to site
>Type up post
>Hit "Post" button
>Browser won't load captcha on that page, so I go to a separate page to solve.
>Solve captcha
>Return to post
>Press "Post" again
>This fucking error message.
AFAIK, the captcha problem and the message are related, because I started seeing the two together at the exact same time. What the fuck am I doing wrong? I've tried restarting my machine, using numerous different browsers, including TOR, turning off my fucking firewall, and probably more shit that I can't remember. What the shit do I do, /wsr/?