I'm pretty sure that the blacklist system has been removed from the plugin.
If you search the plugin code, there's NO cmd or file ref. of blacklist at all, so I think the only way to "blacklist" items is to remove them from the loottable.
It's too bad because a blacklist is an easy way to keep a somewhat dynamic loot on the server and it's much less work than editing every container in the loottable.