[Plugin: Math Comment Spam Protection] Produces error on Comments if user not logged in.

This plugin works just fine in all but one particularly annoying circumstance: Commenting.

When installed, the ONLY way visitors can post comments, is to be “registered” and “logged in”, otherwise they will receive the following error:

Error: Please press the back button and fill the required field for spam protection.

(Note: Pressing the Back button would wipe out their text and force them to re-write it all over again. Annoying & unnecessary.)
I’ve had this problem for what feels like years (back to WP-2.8?), but only just figured out today that this plugin was the source of my problem. Disabling it now allows anyone to comment to my blog once again.

Such a shame. It is otherwise a great plugin, and if you only want Registered users posting, then you won’t care about this bug. Otherwise works with WP-3.3.2.

http://wordpress.org/extend/plugins/math-comment-spam-protection/