Joomla / Virtuemart Timezone Errors

Receiving the following (intermittent) errors in Joomla / Virtuemart for which we need someone to fix asap: Warning: strtotime() [[login to view URL]]: It is not safe to rely on the system's timezone settings. You are *required* to use the [login to view URL] 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 'Africa/Johannesburg' for 'SAST/2.0/no DST' instead in /home/internet/domains/[login to view URL] on line 56 Warning: date() [[login to view URL]]: It is not safe to rely on the system's timezone settings. You are *required* to use the [login to view URL] 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 'Africa/Johannesburg' for 'SAST/2.0/no DST' instead in /home/internet/domains/[login to view URL] on line 198 Warning: Cannot modify header information - headers already sent by (output started at /home/internet/domains/[login to view URL]:56) in /home/internet/domains/[login to view URL] on line 68 Please make backups of any files that are edited. Solution to be documented so that should it happen again we can fix it.