I found that I had a Hook under wp_head with the text: <?php echo ‘<h1>wp_head</h1>’; ?>. It had no effect under v0.3, but appeared under v0.7. Deleted the Hook and all is Ok.
You may want to check the link that appears for GP Hooks on the Plugins page — only when at least one Hook is present (/wp-admin/options-general.php?page=gp_hooks_settings) This gives a 500 error, while the link on the main Dashboard menu is different and gives no error (/wp-admin/themes.php?page=gp_hooks_settings). You may need to change the URL for that first link.