When switching from two distinct moodles on the same server, bad loading relative root reference in server scratches some include_once(...) calls. First symptom is on some typo3 libs as mentionned in thread http://moodle.org/mod/forum/discuss.php?d=71190#318911

This can be fixed in lib/textlib.class.php at §27 as

/// Required files
require_once($CFG->dirroot.'/lib/typo3/class.t3lib_cs.php');
require_once($CFG->dirroot.'/lib/typo3/class.t3lib_div.php');

There may be others...such relative links.