Correct Mantis timezone setting

Warning: strtotime() [function.strtotime]: It is not safe to rely on the system’s timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier.

solution:  Open file , php.ini and enable –   date.timezone = "Asia/Taipei"

Reference from: http://wordpress.org/support/topic/285337