PHP 5.3 changed the PHP configuration requirements for date/timezone handling, and tons of PHP servers are incorrectly configured with invalid (usually missing or number-based instead of name-based) timezones.

If you are getting the following error, you can fix it by creating your own patch files as described below:

Symptom:
PHP Warning: date() [function.date]: 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/New_York' for 'EDT/-5.0/EST' instead in ...

Solution:
Place the following code into 2 NEW files you'll create on your server:
1. /includes/extra_configures/datetime_patch_for_v151_or_older.php
2. /YOUR_ADMIN_FOLDER/includes/extra_configures/datetime_patch_for_v151_or_older.php
NOTE: BOTH files require the same content:
Code:
<?php
/*
 * Get time zone info from PHP config
*/
if (version_compare(PHP_VERSION, 5.3, '>='))
{
  @date_default_timezone_set(date_default_timezone_get());
}

IF THAT DOES NOT WORK, THEN ...
"Plan B" would be to replace date_default_timezone_get() above with your actual timezone like this:

@date_default_timezone_set('Europe/Oslo');


IF THAT STILL DOES NOT WORK ... THEN YOU HAVE A BIGGER SERVER PROBLEM!
If you continue to get errors related to date.timezone after following these instructions, then you must contact your hosting company for help in properly setting date.timezone in your server's PHP configuration. You will have to solve it with their help.