This common WordPress problem most often occurs when adding code snippets to your site via functions.php. Upon reload, instead of your site you see something like the screen above. No good!
To solve it, you should first of all not paste code snippets into your live site! This kind of thing needs to first be tested in a development environment, that’s what it is for. However, if you already see the error above, you will need to go back in and correct whatever is wrong with your syntax.