I've created the web site at http://www.mitreconstruction.co.uk.
This runs WordPress 3.1, the Thematic theme 0.9.7.7 and my own child theme.
Today the client contacted me to say an error was showing at the top of every page.
This only happens in Google Chrome though.
Its basically saying there is an undefined offset in the thematic dynamic-class.php file. I quite new to WordPress, but has anyone else got the same problem, or know how to resolve it.