I just posted this in the BlockNet thread again but I'll post it here too since it's relevant. It seems that pre-version 4 Slayer would default to only allowing the 'actual host' to create a minigame. This can be modified through the settings, but normally that can only be accessed by having permission in the first place. This proves to be a problem for BlockNet clients with rental keys since they can never truly join as the host.
However, you can set the permission preference with this command.
Slayer.Prefs.setPref("Permissions","Create Minigame Rights","1");