Hi - I tried the solution from this post http://www.gravityhelp.com/forums/topic/auto-setting-the-the_post_thumbnail? to auto set the image uploaded to be the featured image. When I do, it crashes my theme and says that the_post_thumbnail is already defined in my wp-includes folder in the page.php file. When I browse my wp-includes folder I don't even see a page.php file, which is odd.
Is this fatal error something to do with my theme do you think? And how could I go about getting this piece of code to take in my functions.php file?