Using different size thumbnails not working

I am trying to creat 4 different types of thumbnails for 4 different custom post types i have made but every time i enter the details for it in the function file, wordpress breaks itself

am i doing something wrong?

// post thumbnail support
	if ( function_exists( ' 250, 250' ) ) add_theme_support( 'post-thumbnails' );

	if ( function_exists( 'add_image_size' ) ) {
	add_image_size( 'news-thumb', 307, 307 );
	add_image_size( 'book-thumb', 450, 900 );
}

any help would be fantastic
Thanks in advance