ajax.php and captcha error

Hi there, I'm having three issues with the plugin.

Firstly, when I tried to submit the form, it gives me the following error from contact-form/scripts/ajax.php.

Failed to load resource: the server responded with a status of 500 (Internal Server Error)

With the above error, no email was sent at all.

Secondly, with reference to the first screenshot, you will notice too that though I did not enable captcha, it still has the reCAPTCHA button.

Finally, with reference to the second screenshot, when I do enable captcha, the whole thing fails altogether (no submit button at all). No error is being printed out on the console.

Hope you will be able to help me with this. Thanks.