Hi
If You have not done any changes to php files than this validation error can't be generated there. I have a copy of this template and can see it without any issues. Most likely the wrong syntax is added in an article or one of the modules. Try disabling all modules and see if problem is there, than republish them one by one checking the site. Last module published till You will be able to see the problem will be to blame and You will need to check it's content closely.