Shabby Chic's included comments section is not compatible with Facebook comments. If you'd like to use Facebook comments, you'll need to replace the current tabbed comments area graphic with an untabbed version and change the organization of the comments area just a bit.
Here's how your new graphic should look:
If you are using the template's default color scheme, you can use the graphic above. Just right click and save the image or grab it however you can in your chosen browser. If you've made color changes to the template, you'll need to produce your own new graphic. If you need to produce your own graphic just open your layout.psd and hide the layer called "Comments" to remove the tabs that show under the "add a comment" and "show X comments" text. Then export your new graphic.
You'll upload the new graphic under ProPhoto 4 --> Customize --> Advanced --> Extra Background Images as both Image #1 and image #2.
Next, go to ProPhoto 4 --> Customize --> Content Appearance --> Call to Action and choose "below comments" for the position of the Call to Action.
That's it! :)