i found the error, not sure is this the main problem.
in assets/js/ciusan-register-login.js
after line 48 'jQuery('p.status', this).show().text(ajax_auth_object.loadingmessage);
there are some variables declared such as –
action = 'ajaxlogin';
username = jQuery('form#login #username').val();
password = jQuery('form#login #password').val();
email = '';
security = jQuery('form#login #security').val();
but the variable ‘recaptcha’ is not declared. So i just declared the variable recaptcha = ”;
then the function working well.