Since yesterday I get this error?

What should I do to solve it?

Thanks so much
Hagen


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 'Europe/Berlin' for 'CET/1.0/no DST' instead in /var/www/vhosts/lvps83-169-44-174.dedicated.hosteurope.de/httpdocs/photo/admin/intro.php on line 128

Warning: mktime() [function.mktime]: 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 'Europe/Berlin' for 'CET/1.0/no DST' instead in /var/www/vhosts/lvps83-169-44-174.dedicated.hosteurope.de/httpdocs/photo/include/functions.inc.php on line 500

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 'Europe/Berlin' for 'CET/1.0/no DST' instead in /var/www/vhosts/lvps83-169-44-174.dedicated.hosteurope.de/httpdocs/photo/include/functions.inc.php on line 500