Here's another nice book companion website.
http://www.fivesimplesteps.co.uk/

Make sure your theme's functions.php file is well formed. I was able to correct this issue by editing my theme's functions.php file. Removing blank lines helped.

I have had this same glitch happen with Wordpress 2.6.3. The fix you've described here has not worked for me. Switching to the default theme made the problem go away but... Once I went back to the first theme, the promlem returned.