Fatal Timezone Error Please Help

[FurryPinups]

Hey all,

I installed Mysidia Adoptables last year and got it working well but went away for other projects in the past 8 months and haven't touched it. I decided to pick it back up and when I went to visit the website it gave me this error.

Warning: Unknown: 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. We selected 'America/Chicago' for 'CDT/-5.0/DST' instead in Unknown on line 0

Fatal error: Uncaught exception 'Exception' with message 'DateTime::__construct() [<a href='datetime.--construct'>datetime.--construct</a>]: 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. We selected 'America/Chicago' for 'CDT/-5.0/DST' instead' in /home1/rad/public_html/pets/classes/class_visitor.php:14 Stack trace: #0 /home1/rad/public_html/pets/classes/class_visitor.php(14): DateTime->__construct() #1 /home1/rad/public_html/pets/classes/class_visitorcreator.php(34): Visitor->__construct('69.15.120.194') #2 /home1/rad/public_html/pets/classes/class_visitorcreator.php(20): VisitorCreator->create_guest() #3 /home1/rad/public_html/pets/classes/class_mysidia.php(273): VisitorCreator->create() #4 /home1/rad/public_html/pets/classes/class_mysidia.php(168): Mysidia->getCurrentUser() #5 /home1/ in /home1/rad/public_html/pets/classes/class_visitor.php on line 14

What does this even mean and how do I fix it? I don't remember a lot of the code or what to do or even the admin panel area since I've been away from it for so long. Any help is appreciated thank you. The website is http://www.pets.furrypinups.com