Site was fresh, instructions were followed exactly. Tried logging out and in, restarting browser and refreshing page (from server and with clear cache). Still, no luck. So it's serverside.
If I'm blocked, it's an error of the captcha network, as I never guess captchas - besides, if blocking users, information on this should be given. Then I could report that mistake.
Photo proof of the entire procedure (or its failure, to be precise) can be seen here: https://imageshack.com/a/HvQz/1

By the way, I'm a programmer myself - PHP, HTML, JS, CSS, learing Ruby on Rails currently. If you need help with that issue or any other part of the game, just PM me (and you've got my email address as well). We'll agree a price (Will work for BTC only).

Or maybe switching the captcha system might be an idea. SolveMedia actually works, just like ReCaptcha. Why reinvent the wheel? Besides they have an (obvious) advantage over your current system.

Forgot to add some debugging info:
Browser: Firefox 34.0.5
OS: Win7 Professional 64bit
System Language: German

Also tried with
Browser: Internet Explorer 11
OS: Windows 8
System Language: German

Any maybe look into encoding. You don't specify one in the form. Just for standard conformism. And perhaps it solves your problem.

BTW, what do you charge for youtube views?