Mike, I sent you a request (and donation) a while back and am looking forward to a response.
Like others, I was receiving a failed CAPTCHA error (“That CAPTCHA was incorrect. Try again.”), but for none of the reasons previously reported (and those threads are all closed).
After much trouble-shooting, including following all efforts step-by-step found at http://www.fastsecurecontactform.com/captcha-always-incorrect, I narrowed it down to one plugin -- Domain Mapping.
After further testing I determined that this issue:
(1) Occurs regardless of theme, folder permissions, etc.;
(2) ONLY occurs on my multi-sites;
(3) ONLY occurs when the parked domain is set as the primary address (via the standard domain mapping plugin)
This makes sense as a session issue, where the cookie is "lost" when the CAPTCHA is processed by the multi-site's domain/subdomain.
I am not sure, but it seems this was not an issue until recently and therefore it MAY be a version issue where it worked and now it doesn't.
The problem is I cannot afford to NOT use the CAPTCHA (serious spam issues these days for many of us), so I'm stuck having the sites resolve to the subdomain, causing confusion to at least one customer and possibly others the longer this sits.
Is there anything you can do? I prefer your plugin over all others, have promoted it to others and from time to time make a donation with the hope I can continue to use your excellent work in the foreseeable future. (I also plan to use the PHP version for non-WordPress sites down the road.)
Ken of Kentropolis