After updating to 2.2.6+ (Build: 20121220) the home page rendering crashes on rendering of Combo List.
Enabling debug at DEVELOPER level will show:
Fatal error: Class 'lang_string' not found in [...]/course/renderer.php on line 126

Possible cause
Line 126 of course/renderer.php is:

  $strinfo = new lang_string('info');

It uses lang_string class not available in Moodle 2.2.x

I guess it was introduced porting fix of MDL-25928 to MOODLE_22_STABLE

Fix
Change line 126 of course/renderer.php to:

  $strinfo = get_string('info');