Over the past 6 months or so, we've had numerous reports of sporadic and non-reproducible errors (to the effect of "Could not open socket") when registering or posting on the forums.
It turns out this is actually being caused by our use of Google's reCAPTCHA service -- these errors occur whenever the reCAPTCHA service becomes unavailable.
To work around this issue, we have modified our forum software to gracefully fall back to its internal CAPTCHA system any time reCAPTCHA is unavailable. You may be asked to resubmit the CAPTCHA letters if this occurs, but that's a better situation than losing your post because of an inexplicable error.
Our apologies to anyone who was impacted by this issue.