existing user login at checkout produce error - "Provided form does not exist"

[kgvconsulting]

New Magento 2.0.2 install, creating user works fine from main / home page and link, however if the existing user add product to cart and attempt log in to their account upon checkout does not work report error: "Provided form does not exist"

Any advise how to fix that?

[Dmitry_Fedyuk · Accepted solution]

Please publish your backend CAPTCHA settings' screenshot.

[kgvconsulting]

Thank you Dimitri, it was the CAPTCHA, now is working fine