Installed this plugin in WordPress 3.0.1 and had the following error on the Tools, Live Countdown Timer page:
-- unserialized string in (my wordpress install directory)/wp-content/plugins/live-countdown-timer/live-countdown-timer.php line 167.
It was an easy fix, just open up live-countdown-timer.php with Notepad and search for this line:
$xDBArr = unserialize(get_option('live_countdown_timer_Values'));
replace the entire line with:
$xDBArr = get_option('live_countdown_timer_Values');
Apparently the data is already unserialized and once you take that out the errors disappear and the plugin works both on the sidebar and the settings.
Just some info to pass along as the author seems to have vanished and his plugin website page is gone and the domain is for sale from what I can tell.