Hello,
To fix that error replace the function "function mail_update_1_2" in plugins/mail/update.php with this one:
function mail_update_1_2() {
DB::execute("UPDATE ".TABLE_PREFIX."tab_panels SET
type = 'plugin',
plugin_id = (SELECT id FROM ".TABLE_PREFIX."plugins WHERE name='mail')
WHERE id='mails-panel'");
}
Don't worry about this issue, it doesn't affect any feature. Mail should be working as usual.
We will be releasing a new version in a few days, if no show-stopper issues are found in these days it will be the 2.1 final.
regards