set_post_thumbnail_size not working

Hi there!

I am loving this wordpress theme and I think the website is becoming something amazing But, I can’t get this part to work. I’ve used these codes for several sites but it’s not working here.

What I want is to create different thumbnail sizes in functions.php and call for the different sizes in the templates/content files!

I use this in functions.php
add_theme_support( ‘page-one-column’ );
set_post_thumbnail_size(‘page-one-column’, 400, 200, true );
add_image_size( ‘page-one-column’, 400, 200, true );

And this in the file where I want this specific thumbnail size to show up:
<?php the_post_thumbnail(‘page-one-column’); ?>

I hope somebody knows the solution to this…