As I'm a developper, my PHP displays notices.
So I get a notice on each instance of JDomHtml.

For example :

Notice: Undefined property: JDomHtmlFormInputSelectCombo::$href in C:\[...]\administrator\components\com_lastevent\dom\html.php on line 148

Just have to delete the unnecesary line 148 : $href = $this->href;

Should be solved now.

Please regenerate.

This notice is still around after regenerating and Joomla 2.5 (project songsheets).
Deleting line 162 (in my case) does only help in frontend, not in backend.

Please check backend of the same project. It is full of notices.