reCAPTCHA not showing

Hi, I have installed your plugin and created a form which includes a reCAPTCHA field. I have entered the public and private key correctly. In the beginning the reCAPTCHA field was showing, but now not any more. I can delete the reCAPTCHA and put it back, but it does not show anymore in the form on my website. Could you please let me know how this is possible and how I can bring it back?

Thanks

Mark

http://wordpress.org/extend/plugins/wordpress-form-manager/