This failure could have been caused by another plugin conflict with this one. If you use CAPTCHA on the login form and ever get locked out due to errors or the CAPTCHA is broken, here is how to get back in:
FTP to your WordPress directory
Delete this folder:
This manually removes the plugin so you should be able to login again.
If you had this problem, please test for a plugin conflict.
First, reinstall the plugin.
This should only take a few minutes.
Here is how to troubleshoot which plugin is conflicting:
Look on the Admin – Plugins – menu.
Temporarily deactivate (not uninstall) all your other plugins. Leave this one still activated.
Does it work now? If yes, activate the other plugins one by one to determine which one conflicts. Test after activating each other plugin. Did that work? Which one was it?