[akanevsky]

Are you sure you are trying to delete THIS hack? I mean, the uninstallation code is:

$db->hide_errors();
$db->query_write("DROP TABLE IF EXISTS " . TABLE_PREFIX . "thanks");

So there is no reason this should cause an error given that (a) the errors are hidden and (b) the table is only deleted if it exists...

EDIT:

I don't know how you have that plugin if you don't have the hack installed (or so it seems), but to be able to access the admincp, put the following line at the end of includes/config.php, right before ?>:
define('DISABLE_HOOKS', true);

Then go to your admincp, remove any plugins you want to remove, then remove the line from config.php.