If you have multisite and see in your error log many
Request exceeded the limit of 80 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://Yoyrsitie/wp-login.php
it is possible that the si-capthca does wrorg request for the .js file.
Solution in file si-capthca.php, function si_captcha_login_head()
Replace line
echo '<script type="text/javascript" src="' . plugins_url('si-captcha-for-wordpress/captcha/si_captcha.js?ver=' . time()) . '"></script>' . "\n";
with the following
echo '<script type="text/javascript" src="' . $this->get_captcha_url_si(). '/si_captcha.js?ver=' . time() . '"></script>';
http://wordpress.org/extend/plugins/si-captcha-for-wordpress/
