Login problem if, Google reCAPTCHA swich on / off
This issue has been fixed in the latest release. The only way to get this problem is having another reCAPTCHA plugin active with wpForo reCAPTCHA. before activating wpForo reCAPTCHA for login an forms make sure you don't have other reCAPTCAH active. In any case if you faced with this should try to login with both:
wpForo Login form: example.com/wp-login.php
WordPress login Form: example.com/community/?wpforo=signin
If both don't work, you should rename the /wpforo/ folder in /wp-content/plugins/ directory. Login disable the reCAPTCHA plugin, rename back to /wpforo/ and activate wpForo plugin. Don't leave wpForo folder renamed.