I have moved my site (drupal 4.5.7) to the new server and now I have this errors in watchdog:

strict warning: date() [function.date]: It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable 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 'Europe/Berlin' for 'CEST/2.0/DST' instead in /home/www/modules/node.module on line 1018.

how should I modify drupal to remove this error?