This is a hosting issue.
In the php.ini file there is a setting for the time zone:
this has been left blank.
you should contact the hosting provider to them update the php.ini file and set the date.timezone setting.
alternately, you could edit the webassist/themes/theme_open.php file and add the following code at line 1 to set the timezone, but it would be better to have it set in the php.ini
<?php date_default_timezone_set('Australia/Perth'); ?>