contact form 7, "captcha":null, without captcha field

Hello

Contact form 7 kept saying it couldn’t send any message…
it checked with firebug, this was my output.
{“mailSent”:false,”into”:”#wpcf7-f9-p223-o1″,”captcha”:null,”message”:”Het bericht kon niet worden verstuurd. Probeer het later nog eens. Of neem telefonisch contact op.”}

the weird thing is I have never set a captcha, is there any place you’d normally set a captcha where I might be able to disable it?

Luke