"Security check" blank error page

Hi,

I have been experiencing random error with the Registration Form.

Basically not consistently 🙁 but often enough to be an issue, upon submission of the form it doesn’t submit and display a blank page with simply: “Security check” at the top and nothing else??

I have disabled plugins / Cache plugin off, , at times it will prove useful, but actually it is still not consistent and it happens the error will popup again.

I realise this is a tricky one, as I am struggling to find a pattern to isolate the issue at this point.

My hope is that it may have happen to someone else and/or someone could point me in the right direction?? Anyone?

URL: http://lescalunetier.com/shop/en/lesca-register-form/

Thanks for reading 🙂

https://wordpress.org/plugins/simplr-registration-form/