I moved an install of a CodeIgniter app from netbook to desktop (both running XAMPP) and notice these peculiar errors started showing up on every page:
A PHP Error was encountered Severity: Warning Message: Unknown: 3 result set(s) not freed. Use mysql_free_result to free result sets which were requested using mysql_query() Filename: Unknown Line Number: 0
Took me a while to figure out but this PHP setting in php.ini was causing the error:
mysql.trace_mode = Off