I thought I had the site figured till I got this. "You can't request more than 20 challenges without solving them. Your previous challenges were flushed."
The challenges you are speaking of a are a part of the captcha system we use - reCaptcha in particular.
Usualy you should be asked only once to enter the captcha code per session. The error you descirbed can be just a hickup of this module, or maybe you just overlooked the captcha input box and tried to submit a comment too many times without entering the proper code.
In any case, the universum will not collapse and the site will remain functional - even if you get cryptic error messages like this.
I'll keep an eye on this issue, chances are we can improve the captcha system in some way.