First off, thank you all for your replies.
second, if i dont use rcon, it says the command is complicated.. or something and see usermanagement help.
Giving a group useradd, should have worked, im guessing ... but it did not. i changed my group to admin, and recieved the same message.
Also in the server logs, i see: Lua error: failed to write /ulib/users.txt --> something along the lines of that, im not viewing the server logs atm, so im not sure exactly. i do know i have permissions to write there, because adv dupe works find, along with straded gamemodes.