Thanks for asking and sorry for the trouble you are facing while validating.
Please make sure that you are using the latest version of X Theme and Cornerstone. As of today the latest version of X Theme and Cornerstone is 6.4.0 and 3.4.0 respectively. While validating, if you are getting any error message then please take a look at following article on common error messages and solution for the same.
In case problem is still there then please share website login details in secure note for us to take a closer look.