The new bodystyles do not rely on permissions, so I see no connection there.
If you want to unselect any of the body styles, just uncheck them (Ctrl - click). No magic and no devling in to files or use of SQL commands required.
There error says that the user does not have permission, so I suggest you start by checking what role the user who got the message was using when the message appeared. Then check the site role definitions (Settings -> Site administration -> Users -> Permissions -> Define roles). Find the role you are interested in and click the "Edit" button. Locate the setting for the "mod/hotpot:attempt" capability, and set it to "Allow". If that was already set to "Allow" then, you'll need to check the Course user permissions in the same way and check that there are no permission overrides.
You can do all of this via the standard Moodle interface. There is no need to "delve into the server files".
Please let us know if checking/changing the permissions resolves the issue for you.