there's an issue with WordPRess 3.0 and tinymcecomments. The version check in
mcecomment_isGreaterThan($ver) is erronous. Therefore the wrong css file is going to be loaded which doesn't exist in WP3.0 and keeps getting filling up the log.
Quick fix in lines 333 and 334:
if ($major == $Cmajor && $minor < $Cminor) return false; if ($major == $Cmajor && $minor == $Cminor && $rev < $Crev) return false;