If you're not using the latest version of the module please download it from here: https://github.com/thirtybees/nocaptcharecaptcha
Prior versions had this issue when you set 0 login attempts in it to skip the contact form checkbox. This was fixed in later versions.
Also I recommend those settings (no spam as of now):
And all the rest to the bottom on YES.
An older version also had this bug where it did not delete it's overwrites and it did show an error related to it. Also if you have a overwrite with the same name already active you have to merge it manually. Or if you had the other recaptcha module (from PS) you need to delete it completely before installing this one (which is better!).