مشکل نصب جوملا

[arash2013]

با سلام
بعد از انتقال سايت جوملا 1.5 به هاست پيام زير را دريافت ميكنم مشكل چيست
توضيح: سرور من مدل nas است :
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 'UTC' for 'GMT/0.0/no DST' instead in /share/MD0_DATA/Web/Joomla/installation/installer/helper.php on line 289

اين مشكل را چگونه حل كنم.
با تشكر آرش