Membership plugin pop up registration form error message "Security check"


I was finishing up my website when I tried to sign up for a free account to test things out. It was working a couple days ago, but now, when I register an account, the pop up shows this simple looking error message "Security check". I'm not sure how to fix it or what went wrong.

I have the plugin set up to redirect to a page once registration is complete, and that does not happen. I un-installed and re-installed the plugin and that does not seem to do anything to help remedy the situation. When I try registering a test account, I click the "Get it Now" button (which is my sign up button), and everything looks great until I click the submit button, and that's when the error message shows up. The account registers, and shows up in the members list, however, not with the corresponding membership group it's supposed to be allotted to ... that field is blank.

The registration page is here:

Thanks for your time and help in advance!