You cannot ban that player/ You cannot kick that player

Whenever I try to ban or kick anyone, on my console or in Minecraft, it says "you cannot ban/kick that player". I have a large amount of plugins and I don't want to post them all because I think that it might have something to do with either essentials or bpermissions, both of which I use. If someone requests, I'll post all of my plugins. Any help would be GREATLY appreciated as it's kind of a big problem as you could probably guess. Thanks