A website I do dev work for just recently went down and when I set WP_DEBUG to true, I got the following error:
Fatal error: Cannot redeclare class bruteprotect_math_authenticate in /wp-content/plugins/bruteprotect/math-fallback.php on line 7
They have the most up-to-date version of BruteProtect installed and the issue happened within the past 3 hours. I believe this started after another person updated BruteProtect to the current version, but I can't confirm that at this time.
To make things stranger, this issue is only happening on the one site, which is also the only site I deal with that is hosted on RackSpace.
Either way, you may want to find out why that issue is occurring. One thing I noticed is that at the start of your plugin, you have
require_once dirname( __FILE__ ) . '/math-fallback.php';, so if this plugin is loaded, math-fallback.php is loaded too, but then you have
include 'math-fallback.php'; in two other places. I might be missing the reason for this, but it doesn't look like it's necessary.