Importing XML To New Site - No Thumbnails

I am trying to have a new user be able to import an xml file to their site right after they sign up. Everything is working fine, but the thumbnails on the front page aren't showing up. They are broken images.

I am using a Studiopress theme which automatically creates the thumbnail for the front page when you add an image to the post. The images are in the post after import, but they are broken on the front page.

Any ideas?