afaik the timezone problem should be solved by now. I encountered this issue on dev.t.o and i18n.t.o. Both sites are now accessible to me (using Win/FF 3.6 und 4.0), IE 7, Chrome). Dev runs now on TW 6.2 and i18n on TW 8.0 (trunk).
Does a fresh and clean install of TW 6.2 work? What's the content of your local_tz cookie? You can try to set another timezone in your tiki.
well it isn't a bad module here it seems or a calendar event. on some of the (test-)systems the calendar feature is disabled and you got the error.
but that March-user-set-timezone-from-germany problem seems to be it.
if i clear my cookies now i have no problems, if i set my date back to march, clear cookies and try to surf on the tiki i have the problem, if i change date back to today, change settings to standard timezone, clear cookies, set date back to march, i have no problems surfing on the tiki.
and thinking of the situation it seems to me that i can surf on all tiki sites again since the beginning of april.