Recaptcha was working and now fails with a HTTP 400 error

[Tony Murphy]

"NetworkError: 400 Bad Request - https://www.google.com/recaptcha/api2/frame?c=03AHJ_VusjTJdhhxX24Xg6YaLcV6Kob...

Recaptcha has stopped working on our website. It was working fine, but since Saturday last, it's broken. 

I suspected it might be an issue with the 

The following script tag

<script src='https://www.google.com/recaptcha/api.js'></script>

is in the head element of the page

and following is part of the form (data-sitekey obviously different)

<div class="g-recaptcha" data-sitekey="xxxxxxxx"></div>

Can someone please help? 

Is there a Google Support account that can help?

[Tony Murphy]

turns out site key was wrapped in quotations and we got 400 errors as a result