I have problems with Google's Captcha system (recaptcha). The problem is that sometimes it is impossible to solve the captcha. I think the problems occurs when you're choosing audio rather than images for solving the captcha. I think it sort off remembers that choice (images or audio challenge) and I usually get this error after I first do an audio challenge first and then the next time I need to solve a captcha.
It usually occurs with filejoker.net and uploadgig.com (maybe more with hosters that use Google's captcha but I haven't checked).
I'm using Chrome with the JD-plugin installed. This problem occures on both my laptop and my desktop.