Some standard commands stopped working

I have a problem with my basic commands like /give and /tp, they stopped working and I don't know how to fix it.

some info about my server that might help: I've installed some plugins and I'm running a 1.12 bukkit server. the /tp command stopped working today

when I try to type these command the chat tells me: an error has occured. see console.

okay, thanks. any way to fix this without having to delete the plugins?

I'll give that a try!

is there anything special I need to do after downloading essentialsX? run a command or just let it do its job?