As I upgraded to 7.3 beta2, my captcha stopped working. I tried regenerating the keys etc... and I finally abandonned after a few hours of trying to understand the dolphin spaghetti code. I removed the captcha from the join form, as well as from forgot.php and contact.php.
You must understand this is such an old captcha and really it would be the bear minimum to upgrade it to v2 for better security too, rather than justifying that it can't be done now "because it is not responsive".
I do find that the lack of "responsive" support is pushing users towards leaving boonex, and it is unfortunate.
Regards,
Marc