I posted in a thread marked resolved so I decided to put this in its own thread. I have definitely had functionality fail after some of the recent updates...
I am also having problems with the plugin since some resent updates. I had no problems with it for a long time and then during a recent push for registrations we were inundated with emails from frustrated users who had the correct answer but validation would fail.
It's been rather hard to debug as the problem is intermittent but I believe I am close to an answer.
I think setting the raw_output parameter to true when creating the $Salt in functions encode and decode are resulting in errors for some browsers. This seems especially true when the captcha answer is one of a larger value, say 9 rather than 2.
In short I am able to replicate the issue with larger answers and the md5 raw output set to true. Setting it to false seems to make the issue go away.
There's definitely an issue with the plugin, I've been working on this for a couple of weeks and this is the closest I've come to certainty as to what is happening.
Hope this helps someone... bestweb I'd be happy to run some debugging with you.
Thanks, I like this plugin and hope to keep using it.