I am sorry. I can't check the plugin with every one of the thousands of plugins out there. I did not know it interfered with a Captcha plugin (there are 302 of them). The message is coming from the captcha plugin and not Stop Spammer Registrations.
Just delete the stop-spammer-registrations-plugin folder from the plugins folder and things should return to normal.
I will add a note to the readme that it may interfere with login plugins, including ones that use CAPTCHA.
Keith P. Graham