I logged into your site and I see the issue you mentioned.
It seems to be part of a larger core WordPress issue.
A lot of other people are having the same issue.
I disabled the plugins which are not required by Integral and tried to edit the hero.php file but it just deletes all the content inside that file and I received the same error message you did.
The only solution I see for now is to edit the file on your computer and upload it via FTP, if you know how to do that. I imagine they will have a fix to this problem once a update to the WordPress core is released.