Theme preview shows blank white screen

I’ve noticed that when trying to preview the Carrington-blog theme, I get a blank white preview. I get the same on WPMU 2.7.1 and WP 2.7.1 installations. I have seen this occasionally on other themes (though not often). The permissions on each theme directory is the same. What might be causing this? I assume preview is not broken for everyone as it’s an obvious bug to spot.

Thanks.