Why might compiling become mysteriously deadlocked ?

This message reports a deadlock due to logitech camera software.

This page, mentioned under internal compiler errors, explains another possible cause.

PHP Warning

lib/XmlElement.php:43 Warning[2]: get_class() expects parameter 1 to be object, string given (...repeated 9 times)

lib/XmlElement.php (In template 'navbar' < 'top' < 'body' < 'html'):43 Warning[2]: get_class() expects parameter 1 to be object, string given:

lib/XmlElement.php (In template 'navbar' < 'top' < 'body' < 'html'):43 Warning[2]: get_class() expects parameter 1 to be object, string given:

lib/XmlElement.php (In template 'browse' < 'body' < 'html'):43 Warning[2]: get_class() expects parameter 1 to be object, string given

Valid XHTML 1.0! Valid CSS!
Page Execution took real: 0.075, user: 0.050, sys: 0.010 seconds , Memory: 2492536

lib/XmlElement.php (In template 'browse' < 'body' < 'html'):43 Warning[2]: get_class() expects parameter 1 to be object, string given

lib/XmlElement.php (In template 'actionbar' < 'browse-footer'):43 Warning[2]: get_class() expects parameter 1 to be object, string given: